diff --git a/background/navigator-util.js b/background/navigator-util.js
index ea233aca..fe573049 100644
--- a/background/navigator-util.js
+++ b/background/navigator-util.js
@@ -14,7 +14,7 @@ const navigatorUtil = (() => {
   }
 
   function initUrlChange() {
-    if (!handler.urlChange) {
+    if (handler.urlChange) {
       return;
     }
     handler.urlChange = [];
diff --git a/background/style-manager.js b/background/style-manager.js
index 3946cd56..ce8fe20f 100644
--- a/background/style-manager.js
+++ b/background/style-manager.js
@@ -37,7 +37,7 @@ const styleManager = (() => {
   });
 
   function handleLivePreviewConnections() {
-    chrome.runtime.onConnect(port => {
+    chrome.runtime.onConnect.addListener(port => {
       if (port.name !== 'livePreview') {
         return;
       }
diff --git a/edit.html b/edit.html
index 4fe6708b..e838a65b 100644
--- a/edit.html
+++ b/edit.html
@@ -137,8 +137,11 @@
 
     <template data-id="section">
       <div class="section">
+        <!-- not using DIV to make our CSS work for #sections > div:only-of-type .remove-section -->
+        <p class="deleted-section">
+          <button class="restore-section" i18n-text="sectionRestore"></button>
+        </p>
         <label i18n-text="sectionCode" class="code-label"></label>
-        <br>
         <div class="applies-to">
           <label i18n-text="appliesLabel">
             <a href="#" class="svg-inline-wrapper applies-to-help" tabindex="0">
@@ -159,13 +162,6 @@
       </div>
     </template>
 
-    <!-- not using DIV to make our CSS work for #sections > div:only-of-type .remove-section -->
-    <template data-id="deletedSection">
-      <p class="deleted-section">
-        <button class="restore-section" i18n-text="sectionRestore"></button>
-      </p>
-    </template>
-
     <template data-id="searchReplaceDialog">
       <div id="search-replace-dialog">
         <div data-type="main">
@@ -291,7 +287,7 @@
       <h1 id="heading">&nbsp;</h1> <!-- nbsp allocates the actual height which prevents page shift -->
       <section id="basic-info">
         <div id="basic-info-name">
-          <input id="name" class="style-contributor" spellcheck="false">
+          <input id="name" class="style-contributor" spellcheck="false" required>
           <a id="url" target="_blank"><svg class="svg-icon"><use xlink:href="#svg-icon-external-link"/></svg></a>
         </div>
         <div id="basic-info-enabled">
diff --git a/edit/beautify.js b/edit/beautify.js
index 50ef5553..92de7509 100644
--- a/edit/beautify.js
+++ b/edit/beautify.js
@@ -4,7 +4,7 @@ global editors getSectionForChild showHelp
 */
 'use strict';
 
-function beautify(event) {
+function beautify(scope) {
   loadScript('/vendor-overwrites/beautify/beautify-css-mod.js')
     .then(() => {
       if (!window.css_beautify && window.exports) {
@@ -22,9 +22,6 @@ function beautify(event) {
     options.indent_size = tabs ? 1 : prefs.get('editor.tabSize');
     options.indent_char = tabs ? '\t' : ' ';
 
-    const section = getSectionForChild(event.target);
-    const scope = section ? [section.CodeMirror] : editors;
-
     showHelp(t('styleBeautify'),
       $create([
         $create('.beautify-options', [
diff --git a/edit/codemirror-editing-hooks.js b/edit/codemirror-editing-hooks.js
index 44c2778d..a76c9c29 100644
--- a/edit/codemirror-editing-hooks.js
+++ b/edit/codemirror-editing-hooks.js
@@ -1,8 +1,7 @@
 /*
 global CodeMirror loadScript
-global editors editor styleId ownTabId
-global save toggleStyle setupAutocomplete makeSectionVisible getSectionForChild
-global getSectionsHashes
+global editor ownTabId
+global save toggleStyle makeSectionVisible
 global messageBox
 */
 'use strict';
@@ -186,8 +185,9 @@ onDOMscriptReady('/codemirror.js').then(() => {
   }
 
   function nextPrevEditor(cm, direction) {
+    const editors = style.getEditors();
     cm = editors[(editors.indexOf(cm) + direction + editors.length) % editors.length];
-    makeSectionVisible(cm);
+    editor.scrollToEditor(cm);
     cm.focus();
     return cm;
   }
@@ -400,8 +400,9 @@ onDOMscriptReady('/codemirror.js').then(() => {
   function closestVisible(nearbyElement) {
     const cm =
       nearbyElement instanceof CodeMirror ? nearbyElement :
-      nearbyElement instanceof Node && (getSectionForChild(nearbyElement) || {}).CodeMirror ||
-      editors.lastActive;
+      nearbyElement instanceof Node &&
+        (nearbyElement.closest('#sections > .section') || {}).CodeMirror ||
+      editor.getLastActivatedEditor();
     if (nearbyElement instanceof Node && cm) {
       const {left, top} = nearbyElement.getBoundingClientRect();
       const bounds = cm.display.wrapper.getBoundingClientRect();
@@ -466,7 +467,7 @@ onDOMscriptReady('/codemirror.js').then(() => {
       }
       const cm = editors[b];
       if (distances[b] > 0) {
-        makeSectionVisible(cm);
+        editor.scrollToEditor(cm);
       }
       return cm;
     }
@@ -588,4 +589,40 @@ onDOMscriptReady('/codemirror.js').then(() => {
     }
     return '';
   }
+
+  function setupAutocomplete(cm, enable = true) {
+    const onOff = enable ? 'on' : 'off';
+    cm[onOff]('changes', autocompleteOnTyping);
+    cm[onOff]('pick', autocompletePicked);
+  }
+
+  function autocompleteOnTyping(cm, [info], debounced) {
+    if (
+      cm.state.completionActive ||
+      info.origin && !info.origin.includes('input') ||
+      !info.text.last
+    ) {
+      return;
+    }
+    if (cm.state.autocompletePicked) {
+      cm.state.autocompletePicked = false;
+      return;
+    }
+    if (!debounced) {
+      debounce(autocompleteOnTyping, 100, cm, [info], true);
+      return;
+    }
+    if (info.text.last.match(/[-a-z!]+$/i)) {
+      cm.state.autocompletePicked = false;
+      cm.options.hintOptions.completeSingle = false;
+      cm.execCommand('autocomplete');
+      setTimeout(() => {
+        cm.options.hintOptions.completeSingle = true;
+      });
+    }
+  }
+
+  function autocompletePicked(cm) {
+    cm.state.autocompletePicked = true;
+  }
 });
diff --git a/edit/edit.css b/edit/edit.css
index 17f630ca..38eee093 100644
--- a/edit/edit.css
+++ b/edit/edit.css
@@ -349,6 +349,18 @@ input:invalid {
 .section:only-of-type .move-section-down {
   display: none;
 }
+/* deleted section */
+.section .deleted-section {
+  display: none;
+}
+.section.removed .deleted-section {
+  display: block;
+}
+.section.removed .code-label,
+.section.removed .applies-to,
+.section.removed .edit-actions {
+  display: none;
+}
 .move-section-up:after {
   content: "";
   display: block;
diff --git a/edit/edit.js b/edit/edit.js
index d1ef3bed..bd6384fc 100644
--- a/edit/edit.js
+++ b/edit/edit.js
@@ -11,21 +11,19 @@ global moveFocus editorWorker msg
 */
 'use strict';
 
-let styleId = null;
-// only the actually dirty items here
-let dirty = {};
-// array of all CodeMirror instances
-const editors = [];
 let saveSizeOnClose;
 let ownTabId;
 
 // direct & reverse mapping of @-moz-document keywords and internal property names
 const propertyToCss = {urls: 'url', urlPrefixes: 'url-prefix', domains: 'domain', regexps: 'regexp'};
-const CssToProperty = {'url': 'urls', 'url-prefix': 'urlPrefixes', 'domain': 'domains', 'regexp': 'regexps'};
+const CssToProperty = Object.entries(propertyToCss)
+  .reduce((o, v) => {
+    o[v[1]] = v[0];
+    return o;
+  }, {});
 
 let editor;
 
-
 document.addEventListener('visibilitychange', beforeUnload);
 msg.onExtension(onRuntimeMessage);
 
@@ -43,21 +41,17 @@ Promise.all([
 
   $('#preview-label').classList.toggle('hidden', !styleId);
 
-  $('#beautify').onclick = beautify;
+  $('#beautify').onclick = () => beautify(editor.getEditors());
   $('#lint').addEventListener('scroll', hideLintHeaderOnScroll, {passive: true});
   window.addEventListener('resize', () => debounce(rememberWindowSize, 100));
 
   exclusions.init(style);
-  if (usercss) {
-    editor = createSourceEditor(style);
-  } else {
-    initWithSectionStyle(style);
-    document.addEventListener('wheel', scrollEntirePageOnCtrlShift);
-  }
+  editor = usercss ? createSourceEditor(style) : createSectionEditor(style);
 });
 
 function preinit() {
   // make querySelectorAll enumeration code readable
+  // FIXME: don't extend native
   ['forEach', 'some', 'indexOf', 'map'].forEach(method => {
     NodeList.prototype[method] = Array.prototype[method];
   });
@@ -168,11 +162,7 @@ function onRuntimeMessage(request) {
           ? API.getStyleFromDB(id)
           : Promise.resolve([request.style])
         ).then(([style]) => {
-          if (isUsercss(style)) {
-            editor.replaceStyle(style, request.codeIsUpdated);
-          } else {
-            initWithSectionStyle(style, request.codeIsUpdated);
-          }
+          editor.replaceStyle(style, request.codeIsUpdated);
         });
       }
       break;
@@ -192,12 +182,6 @@ function onRuntimeMessage(request) {
     case 'editDeleteText':
       document.execCommand('delete');
       break;
-    case 'exclusionsUpdated':
-      debounce(() => exclusions.update({
-        list: Object.keys(request.style.exclusions),
-        isUpdating: false
-      }), 100);
-      break;
   }
 }
 
@@ -217,8 +201,7 @@ function beforeUnload() {
     // refocus if unloading was canceled
     setTimeout(() => activeElement.focus());
   }
-  const isDirty = editor ? editor.isDirty() : !isCleanGlobal();
-  if (isDirty) {
+  if (editor.isDirty()) {
     // neither confirm() nor custom messages work in modern browsers but just in case
     return t('styleChangesNotSaved');
   }
@@ -274,252 +257,6 @@ function initStyleData() {
   }
 }
 
-function initHooks() {
-  if (initHooks.alreadyDone) {
-    return;
-  }
-  initHooks.alreadyDone = true;
-  $$('#header .style-contributor').forEach(node => {
-    node.addEventListener('change', onChange);
-    node.addEventListener('input', onChange);
-  });
-  $('#to-mozilla').addEventListener('click', showMozillaFormat, false);
-  $('#to-mozilla-help').addEventListener('click', showToMozillaHelp, false);
-  $('#from-mozilla').addEventListener('click', fromMozillaFormat);
-  $('#save-button').addEventListener('click', save, false);
-  $('#sections-help').addEventListener('click', showSectionHelp, false);
-
-  if (!FIREFOX) {
-    $$([
-      'input:not([type])',
-      'input[type="text"]',
-      'input[type="search"]',
-      'input[type="number"]',
-    ].join(','))
-      .forEach(e => e.addEventListener('mousedown', toggleContextMenuDelete));
-  }
-}
-
-function getNodeValue(node) {
-  // return length of exclusions; or the node value
-  return node.id === 'excluded-list' ? node.children.length.toString() : node.value;
-}
-
-function onChange(event) {
-  const node = event.target;
-  if ('savedValue' in node) {
-    const currentValue = node.type === 'checkbox' ? node.checked : getNodeValue(node);
-    setCleanItem(node, node.savedValue === currentValue);
-  } else {
-    // the manually added section's applies-to is dirty only when the value is non-empty
-    setCleanItem(node, node.localName !== 'input' || !getNodeValue(node).trim());
-    // only valid when actually saved
-    delete node.savedValue;
-  }
-  updateTitle();
-}
-
-// Set .dirty on stylesheet contributors that have changed
-function setDirtyClass(node, isDirty) {
-  node.classList.toggle('dirty', isDirty);
-}
-
-function setCleanItem(node, isClean) {
-  if (!node.id) {
-    node.id = Date.now().toString(32).substr(-6);
-  }
-
-  if (isClean) {
-    delete dirty[node.id];
-    // code sections have .CodeMirror property
-    if (node.CodeMirror) {
-      node.savedValue = node.CodeMirror.changeGeneration();
-    } else {
-      node.savedValue = node.type === 'checkbox' ? node.checked : getNodeValue(node);
-    }
-  } else {
-    dirty[node.id] = true;
-  }
-
-  setDirtyClass(node, !isClean);
-}
-
-function isCleanGlobal() {
-  const clean = Object.keys(dirty).length === 0;
-  setDirtyClass(document.body, !clean);
-  return clean;
-}
-
-function setCleanGlobal() {
-  setCleanItem($('#sections'), true);
-  $$('#header, #sections > .section').forEach(setCleanSection);
-  // forget the dirty applies-to ids from a deleted section after the style was saved
-  dirty = {};
-}
-
-function setCleanSection(section) {
-  $$('.style-contributor', section).forEach(node => setCleanItem(node, true));
-  setCleanItem(section, true);
-  updateTitle();
-}
-
-function toggleStyle() {
-  $('#enabled').dispatchEvent(new MouseEvent('click', {bubbles: true}));
-}
-
-function save() {
-  if (!validate()) {
-    return;
-  }
-
-  API.editSave({
-    id: styleId,
-    name: $('#name').value.trim(),
-    enabled: $('#enabled').checked,
-    sections: getSectionsHashes(),
-    exclusions: exclusions.get()
-  })
-  .then(style => {
-    styleId = style.id;
-    sessionStorage.justEditedStyleId = styleId;
-    setCleanGlobal();
-    // Go from new style URL to edit style URL
-    if (location.href.indexOf('id=') === -1) {
-      history.replaceState({}, document.title, 'edit.html?id=' + style.id);
-      $('#heading').textContent = t('editStyleHeading');
-    }
-    updateTitle();
-    $('#preview-label').classList.remove('hidden');
-  });
-}
-
-function validate() {
-  const name = $('#name').value.trim();
-  if (!name) {
-    $('#name').focus();
-    messageBox.alert(t('styleMissingName'));
-    return false;
-  }
-
-  if ($$('.applies-to-list li:not(.applies-to-everything)')
-    .some(li => {
-      const type = $('[name=applies-type]', li).value;
-      const value = $('[name=applies-value]', li);
-      const rx = value.value.trim();
-      if (type === 'regexp' && rx && !tryRegExp(rx)) {
-        value.focus();
-        value.select();
-        return true;
-      }
-    })) {
-    messageBox.alert(t('styleBadRegexp'));
-    return false;
-  }
-
-  return true;
-}
-
-function updateTitle() {
-  const name = $('#name').savedValue;
-  const clean = isCleanGlobal();
-  const title = styleId === null ? t('addStyleTitle') : name;
-  document.title = (clean ? '' : '* ') + title;
-  window.onbeforeunload = clean ? null : beforeUnload;
-  $('#save-button').disabled = clean;
-}
-
-function showMozillaFormat() {
-  const popup = showCodeMirrorPopup(t('styleToMozillaFormatTitle'), '', {readOnly: true});
-  popup.codebox.setValue(toMozillaFormat());
-  popup.codebox.execCommand('selectAll');
-}
-
-function toMozillaFormat() {
-  return sectionsToMozFormat({sections: getSectionsHashes()});
-}
-
-function fromMozillaFormat() {
-  const popup = showCodeMirrorPopup(t('styleFromMozillaFormatPrompt'),
-    $create('.buttons', [
-      $create('button', {
-        name: 'import-replace',
-        textContent: t('importReplaceLabel'),
-        title: 'Ctrl-Shift-Enter:\n' + t('importReplaceTooltip'),
-        onclick: () => doImport({replaceOldStyle: true}),
-      }),
-      $create('button', {
-        name: 'import-append',
-        textContent: t('importAppendLabel'),
-        title: 'Ctrl-Enter:\n' + t('importAppendTooltip'),
-        onclick: doImport,
-      }),
-    ]));
-  const contents = $('.contents', popup);
-  contents.insertBefore(popup.codebox.display.wrapper, contents.firstElementChild);
-  popup.codebox.focus();
-  popup.codebox.on('changes', cm => {
-    popup.classList.toggle('ready', !cm.isBlank());
-    cm.markClean();
-  });
-  // overwrite default extraKeys as those are inapplicable in popup context
-  popup.codebox.options.extraKeys = {
-    'Ctrl-Enter': doImport,
-    'Shift-Ctrl-Enter': () => doImport({replaceOldStyle: true}),
-  };
-
-  function doImport({replaceOldStyle = false}) {
-    lockPageUI(true);
-    editorWorker.parseMozFormat({code: popup.codebox.getValue().trim()})
-      .then(({sections, errors}) => {
-        // shouldn't happen but just in case
-        if (!sections.length && errors.length) {
-          return Promise.reject(errors);
-        }
-        // show the errors in case linting is disabled or stylelint misses what csslint has found
-        if (errors.length && prefs.get('editor.linter') !== 'csslint') {
-          showError(errors);
-        }
-        removeOldSections(replaceOldStyle);
-        return addSections(sections, div => setCleanItem(div, false));
-      })
-      .then(() => {
-        $('.dismiss').dispatchEvent(new Event('click'));
-      })
-      .catch(showError)
-      .then(() => lockPageUI(false));
-  }
-
-  function removeOldSections(removeAll) {
-    let toRemove;
-    if (removeAll) {
-      toRemove = editors.slice().reverse();
-    } else if (editors.last.isBlank() && $('.applies-to-everything', editors.last.getSection())) {
-      toRemove = [editors.last];
-    } else {
-      return;
-    }
-    toRemove.forEach(cm => removeSection({target: cm.getSection()}));
-  }
-
-  function lockPageUI(locked) {
-    document.documentElement.style.pointerEvents = locked ? 'none' : '';
-    if (popup.codebox) {
-      popup.classList.toggle('ready', locked ? false : !popup.codebox.isBlank());
-      popup.codebox.options.readOnly = locked;
-      popup.codebox.display.wrapper.style.opacity = locked ? '.5' : '';
-    }
-  }
-
-  function showError(errors) {
-    messageBox({
-      className: 'center danger',
-      title: t('styleFromMozillaFormatError'),
-      contents: $create('pre', Array.isArray(errors) ? errors.join('\n') : errors),
-      buttons: [t('confirmClose')],
-    });
-  }
-}
-
 function showSectionHelp(event) {
   event.preventDefault();
   showHelp(t('styleSectionsTitle'), t('sectionHelp'));
@@ -647,15 +384,6 @@ function setGlobalProgress(done, total) {
   }
 }
 
-function scrollEntirePageOnCtrlShift(event) {
-  // make Shift-Ctrl-Wheel scroll entire page even when mouse is over a code editor
-  if (event.shiftKey && event.ctrlKey && !event.altKey && !event.metaKey) {
-    // Chrome scrolls horizontally when Shift is pressed but on some PCs this might be different
-    window.scrollBy(0, event.deltaX || event.deltaY);
-    event.preventDefault();
-  }
-}
-
 function hideLintHeaderOnScroll() {
   // workaround part2 for the <details> not showing its toggle icon: hide <summary> on scroll
   const newOpacity = this.scrollTop === 0 ? '' : '0';
diff --git a/edit/global-search.js b/edit/global-search.js
index c8bdaa5c..df12a5e3 100644
--- a/edit/global-search.js
+++ b/edit/global-search.js
@@ -314,7 +314,7 @@ onDOMready().then(() => {
       });
       const canFocus = !state.dialog || !state.dialog.contains(document.activeElement);
       makeTargetVisible(!canFocus && input);
-      makeSectionVisible(cm);
+      editor.scrollToEditor(cm);
       if (canFocus) input.focus();
       state.cm = cm;
       clearMarker();
@@ -778,7 +778,7 @@ onDOMready().then(() => {
     cm.scrollIntoView(searchCursor.pos, SCROLL_REVEAL_MIN_PX);
 
     // scroll to the editor itself
-    makeSectionVisible(cm);
+    editor.scrollToEditor(cm);
 
     // focus or expose as the current search target
     clearMarker();
diff --git a/edit/linter-report.js b/edit/linter-report.js
index d12df230..275e9d54 100644
--- a/edit/linter-report.js
+++ b/edit/linter-report.js
@@ -158,7 +158,7 @@ Object.assign(linter, (() => {
   }
 
   function gotoLintIssue(cm, anno) {
-    makeSectionVisible(cm);
+    editor.scrollToEditor(cm);
     cm.focus();
     cm.setSelection(anno.from);
   }
diff --git a/edit/sections-editor.js b/edit/sections-editor.js
new file mode 100644
index 00000000..51ad4ed4
--- /dev/null
+++ b/edit/sections-editor.js
@@ -0,0 +1,771 @@
+/* global dirtyReporter showToMozillaHelp
+  showSectionHelp toggleContextMenuDelete setGlobalProgress maximizeCodeHeight
+  CodeMirror nextPrevEditorOnKeydown showAppliesToHelp propertyToCss
+  regExpTester linter cssToProperty
+*/
+'use strict';
+
+function createResizeGrip(cm) {
+  const wrapper = cm.display.wrapper;
+  wrapper.classList.add('resize-grip-enabled');
+  const resizeGrip = template.resizeGrip.cloneNode(true);
+  wrapper.appendChild(resizeGrip);
+  let lastClickTime = 0;
+  resizeGrip.onmousedown = event => {
+    if (event.button !== 0) {
+      return;
+    }
+    event.preventDefault();
+    if (Date.now() - lastClickTime < 500) {
+      lastClickTime = 0;
+      toggleSectionHeight(cm);
+      return;
+    }
+    lastClickTime = Date.now();
+    const minHeight = cm.defaultTextHeight() +
+      /* .CodeMirror-lines padding */
+      cm.display.lineDiv.offsetParent.offsetTop +
+      /* borders */
+      wrapper.offsetHeight - wrapper.clientHeight;
+    wrapper.style.pointerEvents = 'none';
+    document.body.style.cursor = 's-resize';
+    document.addEventListener('mousemove', resize);
+    document.addEventListener('mouseup', resizeStop);
+
+    function resize(e) {
+      const cmPageY = wrapper.getBoundingClientRect().top + window.scrollY;
+      const height = Math.max(minHeight, e.pageY - cmPageY);
+      if (height !== wrapper.clientHeight) {
+        cm.setSize(null, height);
+      }
+    }
+
+    function resizeStop() {
+      document.removeEventListener('mouseup', resizeStop);
+      document.removeEventListener('mousemove', resize);
+      wrapper.style.pointerEvents = '';
+      document.body.style.cursor = '';
+    }
+  };
+
+  function toggleSectionHeight(cm) {
+    if (cm.state.toggleHeightSaved) {
+      // restore previous size
+      cm.setSize(null, cm.state.toggleHeightSaved);
+      cm.state.toggleHeightSaved = 0;
+    } else {
+      // maximize
+      const wrapper = cm.display.wrapper;
+      const allBounds = $('#sections').getBoundingClientRect();
+      const pageExtrasHeight = allBounds.top + window.scrollY +
+        parseFloat(getComputedStyle($('#sections')).paddingBottom);
+      const sectionExtrasHeight = cm.getSection().clientHeight - wrapper.offsetHeight;
+      cm.state.toggleHeightSaved = wrapper.clientHeight;
+      cm.setSize(null, window.innerHeight - sectionExtrasHeight - pageExtrasHeight);
+      const bounds = cm.getSection().getBoundingClientRect();
+      if (bounds.top < 0 || bounds.bottom > window.innerHeight) {
+        window.scrollBy(0, bounds.top);
+      }
+    }
+  }
+}
+
+function createSectionsEditor(style) {
+  let INC_ID = 0; // an increment id that is used by various object to track the order
+  const dirty = dirtyReporter();
+  dirty.onChange(() => updateTitle);
+
+  const container = $('#sections');
+  const sections = [];
+
+  const nameEl = $('#name');
+  nameEl.addEventListener('change', () => {
+    dirty.modify('name', style.name, nameEl.value);
+    style.name = nameEl.value;
+  });
+
+  const enabledEl = $('#enabled');
+  enabledEl.addEventListener('change', () => {
+    dirty.modify('enabled', style.enabled, enabledEl.checked);
+    style.enabled = enabledEl.checked;
+  });
+
+  $('#to-mozilla').addEventListener('click', showMozillaFormat);
+  $('#to-mozilla-help').addEventListener('click', showToMozillaHelp);
+  $('#from-mozilla').addEventListener('click', fromMozillaFormat);
+  $('#save-button').addEventListener('click', saveStyle);
+  $('#sections-help').addEventListener('click', showSectionHelp);
+
+  document.addEventListener('wheel', scrollEntirePageOnCtrlShift);
+
+  if (!FIREFOX) {
+    $$([
+      'input:not([type])',
+      'input[type="text"]',
+      'input[type="search"]',
+      'input[type="number"]',
+    ].join(','))
+      .forEach(e => e.addEventListener('mousedown', toggleContextMenuDelete));
+  }
+
+  let sectionOrder = '';
+  initSection({
+    sections: style.sections.slice(),
+    done:() => {
+      // FIXME: implement this with CSS?
+      // https://github.com/openstyles/stylus/commit/2895ce11e271788df0e4f7314b3b981fde086574
+      // maximizeCodeHeight(sections[sections.length - 1], true);
+      dirty.clear();
+    }
+  });
+
+  const livePreview = createLivePreview();
+  livePreview.show(Boolean(style.id));
+
+  updateHeader();
+
+  return {
+    replaceStyle,
+    isDirty: dirty.isDirty,
+    getStyle: () => style,
+    getEditors: () =>
+      sections.filter(s => !s.isRemoved()).map(s => s.cm),
+    getLastActivatedEditor,
+    scrollToEditor
+  };
+
+  function scrollToEditor(cm) {
+    const section = sections.find(s => s.cm === cm);
+    const bounds = section.getBoundingClientRect();
+    if (
+      (bounds.bottom > window.innerHeight && bounds.top > 0) ||
+      (bounds.top < 0 && bounds.bottom < window.innerHeight)
+    ) {
+      if (bounds.top < 0) {
+        window.scrollBy(0, bounds.top - 1);
+      } else {
+        window.scrollBy(0, bounds.bottom - window.innerHeight + 1);
+      }
+    }
+  }
+
+  function getLastActivatedEditor() {
+    let result;
+    for (const section of sections) {
+      if (section.isRemoved()) {
+        continue;
+      }
+      if (!result || section.getLastActive() > result.getLastActive) {
+        result = section;
+      }
+    }
+    return result;
+  }
+
+  function nextPrevEditorOnKeydown(cm, event) {
+    const key = event.which;
+    if (key < 37 || key > 40 || event.shiftKey || event.altKey || event.metaKey) {
+      return;
+    }
+    const {line, ch} = cm.getCursor();
+    switch (key) {
+      case 37:
+        // arrow Left
+        if (line || ch) {
+          return;
+        }
+      // fallthrough to arrow Up
+      case 38:
+        // arrow Up
+        if (line > 0 || cm === editors[0]) {
+          return;
+        }
+        event.preventDefault();
+        event.stopPropagation();
+        cm = CodeMirror.commands.prevEditor(cm);
+        cm.setCursor(cm.doc.size - 1, key === 37 ? 1e20 : ch);
+        break;
+      case 39:
+        // arrow Right
+        if (line < cm.doc.size - 1 || ch < cm.getLine(line).length - 1) {
+          return;
+        }
+      // fallthrough to arrow Down
+      case 40:
+        // arrow Down
+        if (line < cm.doc.size - 1 || cm === editors.last) {
+          return;
+        }
+        event.preventDefault();
+        event.stopPropagation();
+        cm = CodeMirror.commands.nextEditor(cm);
+        cm.setCursor(0, 0);
+        break;
+    }
+    const animation = (cm.getSection().firstElementChild.getAnimations() || [])[0];
+    if (animation) {
+      animation.playbackRate = -1;
+      animation.currentTime = 2000;
+      animation.play();
+    }
+  }
+
+  function scrollEntirePageOnCtrlShift(event) {
+    // make Shift-Ctrl-Wheel scroll entire page even when mouse is over a code editor
+    if (event.shiftKey && event.ctrlKey && !event.altKey && !event.metaKey) {
+      // Chrome scrolls horizontally when Shift is pressed but on some PCs this might be different
+      window.scrollBy(0, event.deltaX || event.deltaY);
+      event.preventDefault();
+    }
+  }
+
+  function showMozillaFormat() {
+    const popup = showCodeMirrorPopup(t('styleToMozillaFormatTitle'), '', {readOnly: true});
+    popup.codebox.setValue(sectionsToMozFormat(getModel()));
+    popup.codebox.execCommand('selectAll');
+  }
+
+  function fromMozillaFormat(text = '') {
+    const popup = showCodeMirrorPopup(t('styleFromMozillaFormatPrompt'),
+      $create('.buttons', [
+        $create('button', {
+          name: 'import-replace',
+          textContent: t('importReplaceLabel'),
+          title: 'Ctrl-Shift-Enter:\n' + t('importReplaceTooltip'),
+          onclick: () => doImport({replaceOldStyle: true}),
+        }),
+        $create('button', {
+          name: 'import-append',
+          textContent: t('importAppendLabel'),
+          title: 'Ctrl-Enter:\n' + t('importAppendTooltip'),
+          onclick: doImport,
+        }),
+      ]));
+    const contents = $('.contents', popup);
+    contents.insertBefore(popup.codebox.display.wrapper, contents.firstElementChild);
+    popup.codebox.focus();
+    popup.codebox.on('changes', cm => {
+      popup.classList.toggle('ready', !cm.isBlank());
+      cm.markClean();
+    });
+    if (text) {
+      popup.codebox.setValue(text);
+      popup.codebox.clearHistory();
+      popup.codebox.markClean();
+    }
+    // overwrite default extraKeys as those are inapplicable in popup context
+    popup.codebox.options.extraKeys = {
+      'Ctrl-Enter': doImport,
+      'Shift-Ctrl-Enter': () => doImport({replaceOldStyle: true}),
+    };
+
+    function doImport({replaceOldStyle = false}) {
+      lockPageUI(true);
+      editorWorker.parseMozFormat({code: popup.codebox.getValue().trim()})
+        .then(({sections, errors}) => {
+          // shouldn't happen but just in case
+          if (!sections.length || errors.length) {
+            throw errors;
+          }
+          if (replaceOldStyle) {
+            return replaceSections(sections);
+          }
+          return new Promise(resolve => initSection({sections, done: resolve, focusOn: false}));
+        })
+        .then(() => {
+          $('.dismiss').dispatchEvent(new Event('click'));
+        })
+        .catch(showError)
+        .then(() => lockPageUI(false));
+    }
+
+    function lockPageUI(locked) {
+      document.documentElement.style.pointerEvents = locked ? 'none' : '';
+      if (popup.codebox) {
+        popup.classList.toggle('ready', locked ? false : !popup.codebox.isBlank());
+        popup.codebox.options.readOnly = locked;
+        popup.codebox.display.wrapper.style.opacity = locked ? '.5' : '';
+      }
+    }
+
+    function showError(errors) {
+      messageBox({
+        className: 'center danger',
+        title: t('styleFromMozillaFormatError'),
+        contents: $create('pre', Array.isArray(errors) ? errors.join('\n') : errors),
+        buttons: [t('confirmClose')],
+      });
+    }
+  }
+
+  function updateSectionOrder() {
+    const oldOrder = sectionOrder;
+    const validSections = sections.filter(s => !s.isRemoved());
+    sectionOrder = validSections.map(s => s.id).join(',');
+    dirty.modify('sectionOrder', oldOrder, sectionOrder);
+    container.dataset.sectionCount = validSections.length;
+  }
+
+  function getModel() {
+    return Object.assign({}, style, {
+      sections: sections.map(s => s.getModel())
+    });
+  }
+
+  function validate() {
+    if (!nameEl.reportValidity()) {
+      messageBox.alert(t('styleMissingName'));
+      return false;
+    }
+    for (const section of sections) {
+      for (const apply of section.appliesTo) {
+        if (apply.getType() !== 'regexp') {
+          continue;
+        }
+        if (!apply.valueEl.reportValidity()) {
+          messageBox.alert(t('styleBadRegexp'));
+          return false;
+        }
+      }
+    }
+    return true;
+  }
+
+  function save() {
+    const newStyle = getModel();
+    if (!validate(newStyle)) {
+      return;
+    }
+    API.editSave(newStyle)
+      .then(newStyle => {
+        sessionStorage.justEditedStyleId = newStyle.id;
+        replaceStyle(newStyle);
+      });
+  }
+
+  function updateHeader() {
+    nameEl.value = style.name || '';
+    enabledEl.checked = style.enabled !== false;
+    $('#url').href = style.url || '';
+    updateTitle();
+  }
+
+  function updateLivePreview() {
+    debounce(_updateLivePreview, 200);
+  }
+
+  function _updateLivePreview() {
+    livePreview.update(getModel());
+  }
+
+  function updateTitle() {
+    const name = style.name;
+    const clean = !dirty.isDirty();
+    const title = !style.id ? t('addStyleTitle') : name;
+    document.title = (clean ? '' : '* ') + title;
+    $('#save-button').disabled = clean;
+  }
+
+  function initSection({
+    sections: originalSections,
+    total = originalSections.length,
+    focusOn = 0,
+    done
+  }) {
+    if (!originalSections.length) {
+      setGlobalProgress();
+      if (focusOn !== false) {
+        sections[focusOn].cm.focus();
+      }
+      if (done) {
+        done();
+      }
+      return;
+    }
+    insertSectionAfter(originalSections.shift());
+    setGlobalProgress(total - originalSections.length, total);
+    setTimeout(initSection, 0, {
+      sections: originalSections,
+      total,
+      focusOn,
+      done
+    });
+  }
+
+  function removeSection(section) {
+    if (sections.every(s => s.isRemoved() || s === section)) {
+      throw new Error('Cannot remove last section');
+    }
+    section.remove();
+    if (!section.getCode()) {
+      const index = sections.indexOf(section);
+      sections.splice(index, 1);
+      section.el.remove();
+    } else {
+      const lines = [];
+      const MAX_LINES = 10;
+      section.cm.doc.iter(0, MAX_LINES + 1, ({text}) => lines.push(text) && false);
+      const title = t('sectionCode') + '\n' +
+                   '-'.repeat(20) + '\n' +
+                   lines.slice(0, MAX_LINES).map(s => clipString(s, 100)).join('\n') +
+                   (lines.length > MAX_LINES ? '\n...' : '');
+      $('.deleted-section', section.el).title = title;
+    }
+    dirty.remove(section, section);
+    updateSectionOrder();
+    section.off(updateLivePreview);
+    updateLivePreview();
+  }
+
+  function restoreSection(section) {
+    section.restore();
+    updateSectionOrder();
+    section.onChange(updateLivePreview);
+    updateLivePreview();
+  }
+
+  function insertSectionAfter(init, base) {
+    if (!init) {
+      init = {code: '', urlPrefixes: ['http://example.com']};
+    }
+    const section = createSection(init);
+    container.appendChild(section.el);
+    if (base) {
+      const index = sections.indexOf(base);
+      sections.splice(index, 0, section);
+    } else {
+      sections.push(section);
+    }
+    section.render();
+    // maximizeCodeHeight(section.el);
+    updateSectionOrder();
+    section.onChange(updateLivePreview);
+    updateLivePreview();
+  }
+
+  function moveSectionUp(section) {
+    const index = sections.indexOf(section);
+    if (index === 0) {
+      return;
+    }
+    container.insertBefore(section.el, sections[index - 1].el);
+    sections[index] = sections[index - 1];
+    sections[index - 1] = section;
+    updateSectionOrder();
+  }
+
+  function moveSectionDown(section) {
+    const index = sections.indexOf(section);
+    if (index === sections.length - 1) {
+      return;
+    }
+    container.insertBefore(sections[index + 1].el, section.el);
+    sections[index] = sections[index + 1];
+    sections[index + 1] = section;
+    updateSectionOrder();
+  }
+
+  function createSection(originalSection) {
+    const sectionId = INC_ID++;
+    const el = template.section.cloneNode(true);
+    const cm = CodeMirror(wrapper => {
+      el.insertBefore(wrapper, $('.code-label', el).nextSibling);
+    }, {value: originalSection.code});
+
+    const appliesToContainer = $('.applies-to-list', el);
+    const appliesTo = [];
+    for (const [key, fnName] of Object.entries(propertyToCss)) {
+      if (originalSection[key]) {
+        originalSection[key].forEach(value =>
+          insertApplyAfter({type: fnName, value})
+        );
+      }
+    }
+    if (!appliesTo.length) {
+      const apply = createApply({all: true});
+      appliesTo.push(apply);
+      appliesToContainer.appendChild(apply.el);
+      dirty.addChild(apply.dirty);
+    }
+
+    let changeGeneration = cm.changeGeneration();
+    let removed = false;
+
+    registerEvents();
+    updateRegexpTester();
+    createResizeGrip(cm);
+
+    linter.enableForEditor(cm);
+    linter.refreshReport();
+
+    const changeListeners = new Set();
+
+    let lastActive = 0;
+
+    const section = {
+      id: sectionId,
+      el,
+      cm,
+      render,
+      destroy,
+      getCode,
+      getModel,
+      remove,
+      restore,
+      isRemoved: () => removed,
+      onChange,
+      off,
+      getLastActive: () => lastActive,
+    };
+    return section;
+
+    function onChange(fn) {
+      changeListeners.add(fn);
+    }
+
+    function off(fn) {
+      changeListeners.delete(fn);
+    }
+
+    function emitSectionChange() {
+      for (const fn of changeListeners) {
+        fn();
+      }
+    }
+
+    function getModel() {
+      const section = {
+        code: cm.getValue()
+      };
+      for (const apply of appliesTo) {
+        if (apply.all) {
+          continue;
+        }
+        const key = cssToProperty(apply.getType());
+        if (!section[key]) {
+          section[key] = [];
+        }
+        section[key].push(apply.getValue());
+      }
+      return section;
+    }
+
+    function registerEvents() {
+      cm.on('changes', () => {
+        const newGeneration = cm.changeGeneration();
+        dirty.modify(`section.${sectionId}.code`, changeGeneration, newGeneration);
+        changeGeneration = newGeneration;
+        emitSectionChange();
+      });
+      cm.on('paste', (cm, event) => {
+        const text = event.clipboardData.getData('text') || '';
+        if (
+          text.includes('@-moz-document') &&
+          text.replace(/\/\*[\s\S]*?(?:\*\/|$)/g, '')
+            .match(/@-moz-document[\s\r\n]+(url|url-prefix|domain|regexp)\(/)
+        ) {
+          event.preventDefault();
+          fromMozillaFormat(text);
+        }
+        // FIXME: why?
+        // if (editors.length === 1) {
+          // setTimeout(() => {
+            // if (cm.display.sizer.clientHeight > cm.display.wrapper.clientHeight) {
+              // maximizeCodeHeight.stats = null;
+              // maximizeCodeHeight(cm.getSection(), true);
+            // }
+          // });
+        // }
+      });
+      if (!FIREFOX) {
+        cm.on('mousedown', (cm, event) => toggleContextMenuDelete.call(cm, event));
+      }
+      cm.on('focus', () => lastActive = Date.now());
+
+      cm.display.wrapper.addEventListener('keydown', event =>
+        nextPrevEditorOnKeydown(cm, event), true);
+
+      $('.applies-to-help', el).addEventListener('click', showAppliesToHelp);
+      $('.remove-section', el).addEventListener('click', () => removeSection(section));
+      $('.add-section', el).addEventListener('click', () => insertSectionAfter(undefined, section));
+      $('.clone-section', el).addEventListener('click', () => insertSectionAfter(getModel(), section));
+      $('.move-section-up', el).addEventListener('click', () => moveSectionUp(section));
+      $('.move-section-down', el).addEventListener('click', () => moveSectionDown(section));
+      $('.beautify-section', el).addEventListener('click', () => beautify([cm]));
+      $('.restore-section', el).addEventListener('click', () => restoreSection(section));
+      $('.test-regexp', el).addEventListener('click', () => {
+        regExpTester.toggle();
+        updateRegexpTester();
+      });
+    }
+
+    function getCode() {
+      return cm.getValue();
+    }
+
+    function remove() {
+      linter.disableForEditor(cm);
+      el.classList.add('removed');
+      removed = true;
+      appliesTo.forEach(a => a.remove());
+    }
+
+    function restore() {
+      linter.enableForEditor(cm);
+      el.classList.remove('removed');
+      removed = false;
+      appliesTo.forEach(a => a.restore());
+      render();
+    }
+
+    function render() {
+      cm.refresh();
+    }
+
+    function updateRegexpTester() {
+      const regexps = appliesTo.filter(a => a.getKey() === 'regexp')
+        .map(a => a.getValue());
+      if (regexps.length) {
+        el.classList.add('has-regexp');
+        regExpTester.update(regexps);
+      } else {
+        el.classList.remove('has-regexp');
+        regExpTester.toggle(false);
+      }
+    }
+
+    function insertApplyAfter(init, base) {
+      const apply = createApply(init);
+      if (base) {
+        const index = appliesTo.indexOf(base);
+        appliesTo.splice(index, 0, apply);
+        appliesToContainer.insertBefore(apply.el, base.el.nextSibling);
+      } else {
+        appliesTo.push(apply);
+        appliesToContainer.appendChild(apply.el);
+      }
+      dirty.add(apply, apply);
+      if (appliesTo.length && appliesTo[0].all) {
+        removeApply(appliesTo[0]);
+      }
+      emitSectionChange();
+    }
+
+    function removeApply(apply) {
+      const index = appliesTo.indexOf(apply);
+      appliesTo.splice(index, 1);
+      apply.remove();
+      apply.el.remove();
+      dirty.remove(apply, apply);
+      if (!appliesTo.length) {
+        insertApplyAfter({all: true});
+      }
+      emitSectionChange();
+    }
+
+    function createApply({type, value, all}) {
+      const applyId = INC_ID++;
+      const dirtyPrefix = `section.${sectionId}.apply.${applyId}`;
+      const el = all ? template.appliesToEverything.cloneNode(true) :
+        template.appliesTo.cloneNode(true);
+
+      const selectEl = !all && $('.applies-type', el);
+      if (selectEl) {
+        selectEl.value = type;
+        selectEl.addEventListener('change', () => {
+          const oldKey = type;
+          dirty.modify(`${dirtyPrefix}.type`, type, selectEl.value);
+          type = selectEl.value;
+          if (oldKey === 'regexp' || type === 'regexp') {
+            updateRegexpTester();
+          }
+          emitSectionChange();
+          validate();
+        });
+      }
+
+      const valueEl = !all && $('.applies-value', el);
+      if (valueEl) {
+        valueEl.value = value;
+        valueEl.addEventListener('input', () => {
+          dirty.modify(`${dirtyPrefix}.value`, value, valueEl.value);
+          value = valueEl.value;
+          if (type === 'regexp') {
+            updateRegexpTester();
+          }
+          emitSectionChange();
+        });
+        valueEl.addEventListener('change', validate);
+      }
+
+      const apply = {
+        id: applyId,
+        all,
+        remove,
+        restore,
+        el,
+        getType: () => type,
+        getValue: () => value
+      };
+
+      const removeButton = $('.remove-applies-to', el);
+      if (removeButton) {
+        removeButton.addEventListener('click', () => removeApply(apply));
+      }
+      $('.add-applies-to', el).addEventListener('click', () =>
+        insertApplyAfter({type, value: ''}, apply));
+
+      return apply;
+
+      function validate() {
+        if (type !== 'regexp' || tryRegExp(value)) {
+          valueEl.setCustomValidity('');
+        } else {
+          valueEl.setCustomValidity(t('styleBadRegexp'));
+          setTimeout(() => valueEl.reportValidity());
+        }
+      }
+
+      function remove() {
+        dirty.remove(`${dirtyPrefix}.type`, type);
+        dirty.remove(`${dirtyPrefix}.value`, value);
+      }
+
+      function restore() {
+        dirty.add(`${dirtyPrefix}.type`, type);
+        dirty.add(`${dirtyPrefix}.value`, value);
+      }
+    }
+  }
+
+  function replaceSections(sections) {
+    for (const section of sections) {
+      section.remove();
+    }
+    sections.length = 0;
+    container.textContent = '';
+    return new Promise(resolve => initSection({sections, done: resolve}));
+  }
+
+  function replaceStyle(newStyle, codeIsUpdated) {
+    // FIXME: avoid recreating all editors?
+    reinit().then(() => {
+      style = newStyle;
+      updateHeader();
+      dirty.clear();
+      // Go from new style URL to edit style URL
+      if (location.href.indexOf('id=') === -1 && style.id) {
+        history.replaceState({}, document.title, 'edit.html?id=' + style.id);
+        $('#heading').textContent = t('editStyleHeading');
+      }
+      livePreview.show(Boolean(style.id));
+    });
+
+    function reinit() {
+      if (codeIsUpdated !== false) {
+        return replaceSections(newStyle.sections.slice());
+      }
+      return Promise.resolve();
+    }
+  }
+}
diff --git a/edit/sections.js b/edit/sections.js
deleted file mode 100644
index 44ef3a50..00000000
--- a/edit/sections.js
+++ /dev/null
@@ -1,582 +0,0 @@
-/*
-global CodeMirror
-global editors propertyToCss CssToProperty
-global onChange initHooks setCleanGlobal
-global fromMozillaFormat maximizeCodeHeight toggleContextMenuDelete
-global setCleanItem updateTitle
-global showAppliesToHelp beautify regExpTester setGlobalProgress setCleanSection
-global clipString linter
-*/
-'use strict';
-
-function initWithSectionStyle(style, codeIsUpdated) {
-  $('#name').value = style.name || '';
-  $('#enabled').checked = style.enabled !== false;
-  $('#url').href = style.url || '';
-  if (codeIsUpdated !== false) {
-    editors.length = 0;
-    $('#sections').textContent = '';
-    addSections(style.sections.length ? style.sections : [{code: ''}]);
-    initHooks();
-  }
-  setCleanGlobal();
-  updateTitle();
-}
-
-function addSections(sections, onAdded = () => {}) {
-  if (addSections.running) {
-    console.error('addSections cannot be re-entered: please report to the developers');
-    // TODO: handle this properly e.g. on update/import
-    return;
-  }
-  addSections.running = true;
-  maximizeCodeHeight.stats = null;
-  // make a shallow copy since we might run asynchronously
-  // and the original array might get modified
-  sections = sections.slice();
-  const t0 = performance.now();
-  const divs = [];
-  let index = 0;
-
-  return new Promise(function run(resolve) {
-    while (index < sections.length) {
-      const div = addSection(null, sections[index]);
-      maximizeCodeHeight(div, index === sections.length - 1);
-      onAdded(div, index);
-      divs.push(div);
-      maybeFocusFirstCM();
-      index++;
-      const elapsed = performance.now() - t0;
-      if (elapsed > 500) {
-        setGlobalProgress(index, sections.length);
-      }
-      if (elapsed > 100) {
-        // after 100ms the sections are added asynchronously
-        setTimeout(run, 0, resolve);
-        return;
-      }
-    }
-    editors.last.state.renderLintReportNow = true;
-    addSections.running = false;
-    setGlobalProgress();
-    resolve(divs);
-  });
-
-  function maybeFocusFirstCM() {
-    const isPageLocked = document.documentElement.style.pointerEvents;
-    if (divs[0] && (isPageLocked ? divs.length === sections.length : index === 0)) {
-      makeSectionVisible(divs[0].CodeMirror);
-      setTimeout(() => {
-        if ((document.activeElement || {}).localName !== 'input') {
-          divs[0].CodeMirror.focus();
-        }
-      });
-    }
-  }
-}
-
-function addSection(event, section) {
-  const div = template.section.cloneNode(true);
-  $('.applies-to-help', div).addEventListener('click', showAppliesToHelp);
-  $('.remove-section', div).addEventListener('click', removeSection);
-  $('.add-section', div).addEventListener('click', addSection);
-  $('.clone-section', div).addEventListener('click', cloneSection);
-  $('.move-section-up', div).addEventListener('click', moveSection);
-  $('.move-section-down', div).addEventListener('click', moveSection);
-  $('.beautify-section', div).addEventListener('click', beautify);
-
-  const code = (section || {}).code || '';
-
-  const appliesTo = $('.applies-to-list', div);
-  let appliesToAdded = false;
-
-  if (section) {
-    for (const i in propertyToCss) {
-      if (section[i]) {
-        section[i].forEach(url => {
-          addAppliesTo(appliesTo, propertyToCss[i], url);
-          appliesToAdded = true;
-        });
-      }
-    }
-  }
-  if (!appliesToAdded) {
-    addAppliesTo(appliesTo, event && 'url-prefix', '');
-  }
-
-  appliesTo.addEventListener('change', onChange);
-  appliesTo.addEventListener('input', onChange);
-
-  toggleTestRegExpVisibility();
-  appliesTo.addEventListener('change', toggleTestRegExpVisibility);
-  $('.test-regexp', div).onclick = () => {
-    regExpTester.toggle();
-    regExpTester.update(getRegExps());
-  };
-
-  function getRegExps() {
-    return [...appliesTo.children]
-      .map(item =>
-        !item.matches('.applies-to-everything') &&
-        $('.applies-type', item).value === 'regexp' &&
-        $('.applies-value', item).value.trim()
-      )
-      .filter(item => item);
-  }
-
-  function toggleTestRegExpVisibility() {
-    const show = getRegExps().length > 0;
-    div.classList.toggle('has-regexp', show);
-    appliesTo.oninput = appliesTo.oninput || show && (event => {
-      if (event.target.matches('.applies-value') &&
-          $('.applies-type', event.target.closest('.applies-to-item')).value === 'regexp') {
-        regExpTester.update(getRegExps());
-      }
-    });
-  }
-
-  const sections = $('#sections');
-  let cm;
-  if (event) {
-    let clickedSection = event && getSectionForChild(event.target, {includeDeleted: true});
-    clickedSection.insertAdjacentElement('afterend', div);
-    while (clickedSection && !clickedSection.matches('.section')) {
-      clickedSection = clickedSection.previousElementSibling;
-    }
-    const newIndex = getSections().indexOf(clickedSection) + 1;
-    cm = setupCodeMirror(div, code, newIndex);
-    makeSectionVisible(cm);
-    cm.focus();
-  } else {
-    sections.appendChild(div);
-    cm = setupCodeMirror(div, code);
-  }
-  linter.enableForEditor(cm);
-  linter.refreshReport();
-  div.CodeMirror = cm;
-  setCleanSection(div);
-  return div;
-}
-
-// may be invoked as a DOM listener
-function addAppliesTo(list, type, value) {
-  let clickedItem;
-  if (this instanceof Node) {
-    clickedItem = this.closest('.applies-to-item');
-    list = this.closest('.applies-to-list');
-    // dummy <a> wrapper was clicked
-    if (arguments[0] instanceof Event) arguments[0].preventDefault();
-  }
-  const showingEverything = $('.applies-to-everything', list);
-  // blow away 'Everything' if it's there
-  if (showingEverything) {
-    list.removeChild(list.firstChild);
-  }
-  let item, toFocus;
-
-  // a section is added with known applies-to
-  if (type) {
-    item = template.appliesTo.cloneNode(true);
-    $('[name=applies-type]', item).value = type;
-    $('[name=applies-value]', item).value = value;
-    $('.remove-applies-to', item).addEventListener('click', removeAppliesTo);
-
-  // a "+" button was clicked
-  } else if (showingEverything || clickedItem) {
-    item = template.appliesTo.cloneNode(true);
-    toFocus = $('[name=applies-type]', item);
-    if (clickedItem) {
-      $('[name=applies-type]', item).value = $('[name="applies-type"]', clickedItem).value;
-    }
-    $('.remove-applies-to', item).addEventListener('click', removeAppliesTo);
-
-  // a global section is added
-  } else {
-    item = template.appliesToEverything.cloneNode(true);
-  }
-
-  $('.add-applies-to', item).addEventListener('click', addAppliesTo);
-  list.insertBefore(item, clickedItem && clickedItem.nextElementSibling);
-  if (toFocus) toFocus.focus();
-}
-
-function cloneSection(event) {
-  const section = getSectionForChild(event.target);
-  addSection(event, getSectionsHashes([section]).pop());
-  setCleanItem($('#sections'), false);
-  updateTitle();
-}
-
-function moveSection(event) {
-  const section = getSectionForChild(event.target);
-  const dir = event.target.closest('.move-section-up') ? -1 : 1;
-  const cm = section.CodeMirror;
-  const index = editors.indexOf(cm);
-  const newIndex = (index + dir + editors.length) % editors.length;
-  const currentNextEl = section.nextElementSibling;
-  const newSection = editors[newIndex].getSection();
-  newSection.insertAdjacentElement('afterend', section);
-  section.parentNode.insertBefore(newSection, currentNextEl || null);
-  cm.focus();
-  editors[index] = editors[newIndex];
-  editors[newIndex] = cm;
-  setCleanItem($('#sections'), false);
-  updateTitle();
-}
-
-function setupCodeMirror(sectionDiv, code, index = editors.length) {
-  const cm = CodeMirror(wrapper => {
-    $('.code-label', sectionDiv).insertAdjacentElement('afterend', wrapper);
-  }, {
-    value: code,
-  });
-  const wrapper = cm.display.wrapper;
-
-  let onChangeTimer;
-  cm.on('changes', (cm, changes) => {
-    clearTimeout(onChangeTimer);
-    onChangeTimer = setTimeout(indicateCodeChange, 200, cm, changes);
-  });
-  wrapper.addEventListener('keydown', event => nextPrevEditorOnKeydown(cm, event), true);
-  cm.on('paste', (cm, event) => {
-    const text = event.clipboardData.getData('text') || '';
-    if (
-      text.includes('@-moz-document') &&
-      text.replace(/\/\*[\s\S]*?(?:\*\/|$)/g, '')
-        .match(/@-moz-document[\s\r\n]+(url|url-prefix|domain|regexp)\(/)
-    ) {
-      event.preventDefault();
-      fromMozillaFormat();
-      $('#help-popup').codebox.setValue(text);
-      $('#help-popup').codebox.clearHistory();
-      $('#help-popup').codebox.markClean();
-    }
-    if (editors.length === 1) {
-      setTimeout(() => {
-        if (cm.display.sizer.clientHeight > cm.display.wrapper.clientHeight) {
-          maximizeCodeHeight.stats = null;
-          maximizeCodeHeight(cm.getSection(), true);
-        }
-      });
-    }
-  });
-  if (!FIREFOX) {
-    cm.on('mousedown', (cm, event) => toggleContextMenuDelete.call(cm, event));
-  }
-
-  wrapper.classList.add('resize-grip-enabled');
-  let lastClickTime = 0;
-  const resizeGrip = wrapper.appendChild(template.resizeGrip.cloneNode(true));
-  resizeGrip.onmousedown = event => {
-    if (event.button !== 0) {
-      return;
-    }
-    event.preventDefault();
-    if (Date.now() - lastClickTime < 500) {
-      lastClickTime = 0;
-      toggleSectionHeight(cm);
-      return;
-    }
-    lastClickTime = Date.now();
-    const minHeight = cm.defaultTextHeight() +
-      /* .CodeMirror-lines padding */
-      cm.display.lineDiv.offsetParent.offsetTop +
-      /* borders */
-      wrapper.offsetHeight - wrapper.clientHeight;
-    wrapper.style.pointerEvents = 'none';
-    document.body.style.cursor = 's-resize';
-    function resize(e) {
-      const cmPageY = wrapper.getBoundingClientRect().top + window.scrollY;
-      const height = Math.max(minHeight, e.pageY - cmPageY);
-      if (height !== wrapper.clientHeight) {
-        cm.setSize(null, height);
-      }
-    }
-    document.addEventListener('mousemove', resize);
-    document.addEventListener('mouseup', function resizeStop() {
-      document.removeEventListener('mouseup', resizeStop);
-      document.removeEventListener('mousemove', resize);
-      wrapper.style.pointerEvents = '';
-      document.body.style.cursor = '';
-    });
-  };
-
-  editors.splice(index, 0, cm);
-  return cm;
-}
-
-function indicateCodeChange(cm) {
-  const section = cm.getSection();
-  setCleanItem(section, cm.isClean(section.savedValue));
-  updateTitle();
-}
-
-function setupAutocomplete(cm, enable = true) {
-  const onOff = enable ? 'on' : 'off';
-  cm[onOff]('changes', autocompleteOnTyping);
-  cm[onOff]('pick', autocompletePicked);
-}
-
-function autocompleteOnTyping(cm, [info], debounced) {
-  if (
-    cm.state.completionActive ||
-    info.origin && !info.origin.includes('input') ||
-    !info.text.last
-  ) {
-    return;
-  }
-  if (cm.state.autocompletePicked) {
-    cm.state.autocompletePicked = false;
-    return;
-  }
-  if (!debounced) {
-    debounce(autocompleteOnTyping, 100, cm, [info], true);
-    return;
-  }
-  if (info.text.last.match(/[-a-z!]+$/i)) {
-    cm.state.autocompletePicked = false;
-    cm.options.hintOptions.completeSingle = false;
-    cm.execCommand('autocomplete');
-    setTimeout(() => {
-      cm.options.hintOptions.completeSingle = true;
-    });
-  }
-}
-
-function autocompletePicked(cm) {
-  cm.state.autocompletePicked = true;
-}
-
-function nextPrevEditorOnKeydown(cm, event) {
-  const key = event.which;
-  if (key < 37 || key > 40 || event.shiftKey || event.altKey || event.metaKey) {
-    return;
-  }
-  const {line, ch} = cm.getCursor();
-  switch (key) {
-    case 37:
-      // arrow Left
-      if (line || ch) {
-        return;
-      }
-    // fallthrough to arrow Up
-    case 38:
-      // arrow Up
-      if (line > 0 || cm === editors[0]) {
-        return;
-      }
-      event.preventDefault();
-      event.stopPropagation();
-      cm = CodeMirror.commands.prevEditor(cm);
-      cm.setCursor(cm.doc.size - 1, key === 37 ? 1e20 : ch);
-      break;
-    case 39:
-      // arrow Right
-      if (line < cm.doc.size - 1 || ch < cm.getLine(line).length - 1) {
-        return;
-      }
-    // fallthrough to arrow Down
-    case 40:
-      // arrow Down
-      if (line < cm.doc.size - 1 || cm === editors.last) {
-        return;
-      }
-      event.preventDefault();
-      event.stopPropagation();
-      cm = CodeMirror.commands.nextEditor(cm);
-      cm.setCursor(0, 0);
-      break;
-  }
-  const animation = (cm.getSection().firstElementChild.getAnimations() || [])[0];
-  if (animation) {
-    animation.playbackRate = -1;
-    animation.currentTime = 2000;
-    animation.play();
-  }
-}
-
-function toggleSectionHeight(cm) {
-  if (cm.state.toggleHeightSaved) {
-    // restore previous size
-    cm.setSize(null, cm.state.toggleHeightSaved);
-    cm.state.toggleHeightSaved = 0;
-  } else {
-    // maximize
-    const wrapper = cm.display.wrapper;
-    const allBounds = $('#sections').getBoundingClientRect();
-    const pageExtrasHeight = allBounds.top + window.scrollY +
-      parseFloat(getComputedStyle($('#sections')).paddingBottom);
-    const sectionExtrasHeight = cm.getSection().clientHeight - wrapper.offsetHeight;
-    cm.state.toggleHeightSaved = wrapper.clientHeight;
-    cm.setSize(null, window.innerHeight - sectionExtrasHeight - pageExtrasHeight);
-    const bounds = cm.getSection().getBoundingClientRect();
-    if (bounds.top < 0 || bounds.bottom > window.innerHeight) {
-      window.scrollBy(0, bounds.top);
-    }
-  }
-}
-
-function getSectionForChild(el, {includeDeleted} = {}) {
-  return el.closest(`#sections > ${includeDeleted ? '*' : '.section'}`);
-}
-
-function getSections() {
-  return $$('#sections > .section');
-}
-
-function getSectionsHashes(elements = getSections()) {
-  const sections = [];
-  for (const div of elements) {
-    const meta = {urls: [], urlPrefixes: [], domains: [], regexps: []};
-    for (const li of $('.applies-to-list', div).childNodes) {
-      if (li.className === template.appliesToEverything.className) {
-        break;
-      }
-      const type = $('[name=applies-type]', li).value;
-      const value = $('[name=applies-value]', li).value;
-      if (type && value) {
-        meta[CssToProperty[type]].push(value);
-      }
-    }
-    const code = div.CodeMirror.getValue();
-    if (/^\s*$/.test(code) && Object.keys(meta).length === 0) {
-      continue;
-    }
-    meta.code = code;
-    sections.push(meta);
-  }
-  return sections;
-}
-
-function removeAppliesTo(event) {
-  event.preventDefault();
-  const appliesTo = event.target.closest('.applies-to-item');
-  const appliesToList = appliesTo.closest('.applies-to-list');
-  removeAreaAndSetDirty(appliesTo);
-  if (!appliesToList.hasChildNodes()) {
-    addAppliesTo(appliesToList);
-  }
-}
-
-function removeSection(event) {
-  const section = getSectionForChild(event.target);
-  const cm = section.CodeMirror;
-  if (event instanceof Event && (!cm.isClean() || !cm.isBlank())) {
-    const stub = template.deletedSection.cloneNode(true);
-    const MAX_LINES = 10;
-    const lines = [];
-    cm.doc.iter(0, MAX_LINES + 1, ({text}) => lines.push(text) && false);
-    stub.title = t('sectionCode') + '\n' +
-                 '-'.repeat(20) + '\n' +
-                 lines.slice(0, MAX_LINES).map(s => clipString(s, 100)).join('\n') +
-                 (lines.length > MAX_LINES ? '\n...' : '');
-    $('.restore-section', stub).onclick = () => {
-      let el = stub;
-      while (el && !el.matches('.section')) {
-        el = el.previousElementSibling;
-      }
-      const index = el ? editors.indexOf(el) + 1 : 0;
-      editors.splice(index, 0, cm);
-      stub.parentNode.replaceChild(section, stub);
-      setCleanItem(section, false);
-      updateTitle();
-      cm.focus();
-      linter.enableForEditor(cm);
-      linter.refreshReport();
-    };
-    section.insertAdjacentElement('afterend', stub);
-  }
-  setCleanItem($('#sections'), false);
-  removeAreaAndSetDirty(section);
-  editors.splice(editors.indexOf(cm), 1);
-  linter.disableForEditor(cm);
-  linter.refreshReport();
-}
-
-function removeAreaAndSetDirty(area) {
-  const contributors = $$('.style-contributor', area);
-  if (!contributors.length) {
-    setCleanItem(area, false);
-  }
-  contributors.some(node => {
-    if (node.savedValue) {
-      // it's a saved section, so make it dirty and stop the enumeration
-      setCleanItem(area, false);
-      return true;
-    } else {
-      // it's an empty section, so undirty the applies-to items,
-      // otherwise orphaned ids would keep the style dirty
-      setCleanItem(node, true);
-    }
-  });
-  updateTitle();
-  area.remove();
-}
-
-function makeSectionVisible(cm) {
-  if (editors.length === 1) {
-    return;
-  }
-  const section = cm.getSection();
-  const bounds = section.getBoundingClientRect();
-  if (
-    (bounds.bottom > window.innerHeight && bounds.top > 0) ||
-    (bounds.top < 0 && bounds.bottom < window.innerHeight)
-  ) {
-    if (bounds.top < 0) {
-      window.scrollBy(0, bounds.top - 1);
-    } else {
-      window.scrollBy(0, bounds.bottom - window.innerHeight + 1);
-    }
-  }
-}
-
-function maximizeCodeHeight(sectionDiv, isLast) {
-  const cm = sectionDiv.CodeMirror;
-  const stats = maximizeCodeHeight.stats = maximizeCodeHeight.stats || {totalHeight: 0, deltas: []};
-  if (!stats.cmActualHeight) {
-    stats.cmActualHeight = getComputedHeight(cm.display.wrapper);
-  }
-  if (!stats.sectionMarginTop) {
-    stats.sectionMarginTop = parseFloat(getComputedStyle(sectionDiv).marginTop);
-  }
-  const sectionTop = sectionDiv.getBoundingClientRect().top - stats.sectionMarginTop;
-  if (!stats.firstSectionTop) {
-    stats.firstSectionTop = sectionTop;
-  }
-  const extrasHeight = getComputedHeight(sectionDiv) - stats.cmActualHeight;
-  const cmMaxHeight = window.innerHeight - extrasHeight - sectionTop - stats.sectionMarginTop;
-  const cmDesiredHeight = cm.display.sizer.clientHeight + 2 * cm.defaultTextHeight();
-  const cmGrantableHeight = Math.max(stats.cmActualHeight, Math.min(cmMaxHeight, cmDesiredHeight));
-  stats.deltas.push(cmGrantableHeight - stats.cmActualHeight);
-  stats.totalHeight += cmGrantableHeight + extrasHeight;
-  if (!isLast) {
-    return;
-  }
-  stats.totalHeight += stats.firstSectionTop;
-  if (stats.totalHeight <= window.innerHeight) {
-    editors.forEach((cm, index) => {
-      cm.setSize(null, stats.deltas[index] + stats.cmActualHeight);
-    });
-    return;
-  }
-  // scale heights to fill the gap between last section and bottom edge of the window
-  const sections = $('#sections');
-  const available = window.innerHeight - sections.getBoundingClientRect().bottom -
-    parseFloat(getComputedStyle(sections).marginBottom);
-  if (available <= 0) {
-    return;
-  }
-  const totalDelta = stats.deltas.reduce((sum, d) => sum + d, 0);
-  const q = available / totalDelta;
-  const baseHeight = stats.cmActualHeight - stats.sectionMarginTop;
-  stats.deltas.forEach((delta, index) => {
-    editors[index].setSize(null, baseHeight + Math.floor(q * delta));
-  });
-
-  function getComputedHeight(el) {
-    const compStyle = getComputedStyle(el);
-    return el.getBoundingClientRect().height +
-      parseFloat(compStyle.marginTop) + parseFloat(compStyle.marginBottom);
-  }
-}
diff --git a/edit/source-editor.js b/edit/source-editor.js
index d876d5a4..09e21619 100644
--- a/edit/source-editor.js
+++ b/edit/source-editor.js
@@ -405,5 +405,8 @@ function createSourceEditor(style) {
     replaceStyle,
     isDirty: dirty.isDirty,
     getStyle: () => style,
+    getEditors: () => [cm],
+    getLastActivatedEditor: () => cm,
+    scrollToEditor: () => {}
   };
 }