diff --git a/edit/edit.js b/edit/edit.js
index f13c300c..08cab747 100644
--- a/edit/edit.js
+++ b/edit/edit.js
@@ -103,7 +103,6 @@ lazyInit();
   await editor.ready;
   editor.ready = true;
 
-  setTimeout(() => editor.getEditors().forEach(linter.enableForEditor));
   // enabling after init to prevent flash of validation failure on an empty name
   $('#name').required = !editor.isUsercss;
   $('#save-button').onclick = editor.save;
diff --git a/edit/editor-worker.js b/edit/editor-worker.js
index 9a0ec6fd..559f9aaf 100644
--- a/edit/editor-worker.js
+++ b/edit/editor-worker.js
@@ -4,6 +4,7 @@
 importScripts('/js/worker-util.js');
 const {loadScript} = workerUtil;
 
+/** @namespace EditorWorker */
 workerUtil.createAPI({
   csslint: (code, config) => {
     loadScript('/vendor-overwrites/csslint/parserlib.js', '/vendor-overwrites/csslint/csslint.js');
diff --git a/edit/linter.js b/edit/linter.js
index 52a525b8..35ad28a0 100644
--- a/edit/linter.js
+++ b/edit/linter.js
@@ -2,6 +2,7 @@
 'use strict';
 
 /* exported editorWorker */
+/** @type {EditorWorker} */
 const editorWorker = workerUtil.createWorker({
   url: '/edit/editor-worker.js',
 });
@@ -14,20 +15,57 @@ const linter = (() => {
   const cms = new Set();
 
   return {
-    register,
-    run,
-    enableForEditor,
-    disableForEditor,
-    onLintingUpdated,
-    onUnhook,
+    disableForEditor(cm) {
+      cm.setOption('lint', false);
+      cms.delete(cm);
+      for (const cb of unhookListeners) {
+        cb(cm);
+      }
+    },
+    /**
+     * @param {Object} cm
+     * @param {string} [code] - to be used to avoid slowdowns when creating a lot of cms.
+     * Enables lint option only if there are problems, thus avoiding a _very_ costly layout
+     * update when lint gutter is added to a lot of editors simultaneously.
+     */
+    enableForEditor(cm, code) {
+      if (code) return enableOnProblems(cm, code);
+      cm.setOption('lint', {getAnnotations, onUpdateLinting});
+      cms.add(cm);
+    },
+    onLintingUpdated(cb) {
+      lintingUpdatedListeners.push(cb);
+    },
+    onUnhook(cb) {
+      unhookListeners.push(cb);
+    },
+    register(linterFn) {
+      linters.push(linterFn);
+    },
+    run() {
+      for (const cm of cms) {
+        cm.performLint();
+      }
+    },
   };
 
-  function onUnhook(cb) {
-    unhookListeners.push(cb);
+  async function enableOnProblems(cm, code) {
+    const results = await getAnnotations(code, {}, cm);
+    if (results.length) {
+      cms.add(cm);
+      cm.setOption('lint', {
+        getAnnotations() {
+          cm.options.lint.getAnnotations = getAnnotations;
+          return results;
+        },
+        onUpdateLinting,
+      });
+    }
   }
 
-  function onLintingUpdated(cb) {
-    lintingUpdatedListeners.push(cb);
+  async function getAnnotations(...args) {
+    const results = await Promise.all(linters.map(fn => fn(...args)));
+    return [].concat(...results.filter(Boolean));
   }
 
   function onUpdateLinting(...args) {
@@ -35,32 +73,4 @@ const linter = (() => {
       cb(...args);
     }
   }
-
-  function enableForEditor(cm) {
-    cm.setOption('lint', {onUpdateLinting, getAnnotations});
-    cms.add(cm);
-  }
-
-  function disableForEditor(cm) {
-    cm.setOption('lint', false);
-    cms.delete(cm);
-    for (const cb of unhookListeners) {
-      cb(cm);
-    }
-  }
-
-  function register(linterFn) {
-    linters.push(linterFn);
-  }
-
-  function run() {
-    for (const cm of cms) {
-      cm.performLint();
-    }
-  }
-
-  function getAnnotations(...args) {
-    return Promise.all(linters.map(fn => fn(...args)))
-      .then(results => [].concat(...results.filter(Boolean)));
-  }
 })();
diff --git a/edit/sections-editor.js b/edit/sections-editor.js
index 0bda2466..4130b7c3 100644
--- a/edit/sections-editor.js
+++ b/edit/sections-editor.js
@@ -487,7 +487,7 @@ function SectionsEditor() {
     livePreview.update(getModel());
   }
 
-  function initSections(src, {
+  async function initSections(src, {
     focusOn = 0,
     replace = false,
     pristine = false,
@@ -497,10 +497,6 @@ function SectionsEditor() {
       sections.length = 0;
       container.textContent = '';
     }
-    let done;
-    let index = 0;
-    let y = 0;
-    const total = src.length;
     let si = editor.scrollInfo;
     if (si && si.cms && si.cms.length === src.length) {
       si.scrollY2 = si.scrollY + window.innerHeight;
@@ -510,29 +506,27 @@ function SectionsEditor() {
     } else {
       si = null;
     }
-    return new Promise(resolve => {
-      done = resolve;
-      chunk(!si);
-    });
-    function chunk(forceRefresh) {
-      const t0 = performance.now();
-      while (index < total && performance.now() - t0 < 100) {
-        if (si) forceRefresh = y < si.scrollY2 && (y += si.cms[index].parentHeight) > si.scrollY;
-        insertSectionAfter(src[index], undefined, forceRefresh, si && si.cms[index]);
-        if (pristine) dirty.clear();
-        if (index === focusOn && !si) sections[index].cm.focus();
-        index++;
-      }
-      setGlobalProgress(index, total);
-      if (index === total) {
-        setGlobalProgress();
-        if (!si) requestAnimationFrame(fitToAvailableSpace);
-        container.style.removeProperty('height');
-        done();
-      } else {
-        setTimeout(chunk);
+    let forceRefresh = true;
+    let y = 0;
+    let tPrev;
+    for (let i = 0; i < src.length; i++) {
+      const t = performance.now();
+      if (!tPrev) {
+        tPrev = t;
+      } else if (t - tPrev > 100) {
+        tPrev = 0;
+        forceRefresh = false;
+        await new Promise(setTimeout);
       }
+      if (si) forceRefresh = y < si.scrollY2 && (y += si.cms[i].parentHeight) > si.scrollY;
+      insertSectionAfter(src[i], null, forceRefresh, si && si.cms[i]);
+      setGlobalProgress(i, src.length);
+      if (pristine) dirty.clear();
+      if (i === focusOn && !si) sections[i].cm.focus();
     }
+    if (!si) requestAnimationFrame(fitToAvailableSpace);
+    container.style.removeProperty('height');
+    setGlobalProgress();
   }
 
   /** @param {EditorSection} section */
@@ -584,23 +578,23 @@ function SectionsEditor() {
     }
     const section = createSection(init, genId, si);
     const {cm} = section;
+    const {code} = init;
     const index = base ? sections.indexOf(base) + 1 : sections.length;
     sections.splice(index, 0, section);
     container.insertBefore(section.el, base ? base.el.nextSibling : null);
-    refreshOnView(cm, base || forceRefresh);
+    refreshOnView(cm, {code, force: base || forceRefresh});
     registerEvents(section);
-    if ((!si || !si.height) && (!base || init.code)) {
+    if ((!si || !si.height) && (!base || code)) {
       // Fit a) during startup or b) when the clone button is clicked on a section with some code
       fitToContent(section);
     }
     if (base) {
       cm.focus();
       editor.scrollToEditor(cm);
-      linter.enableForEditor(cm);
     }
     updateSectionOrder();
-    section.onChange(updateLivePreview);
     updateLivePreview();
+    section.onChange(updateLivePreview);
   }
 
   /** @param {EditorSection} section */
@@ -654,10 +648,12 @@ function SectionsEditor() {
     }
   }
 
-  function refreshOnView(cm, force) {
-    return force || !xo ?
-      cm.refresh() :
+  function refreshOnView(cm, {code, force} = {}) {
+    if (force || !xo) {
+      refreshOnViewNow(cm, code);
+    } else {
       xo.observe(cm.display.wrapper);
+    }
   }
 
   /** @param {IntersectionObserverEntry[]} entries */
@@ -668,14 +664,19 @@ function SectionsEditor() {
         xo.unobserve(e.target);
         const cm = e.target.CodeMirror;
         if (r.bottom > 0 && r.top < window.innerHeight) {
-          cm.refresh();
+          refreshOnViewNow(cm);
         } else {
-          setTimeout(() => cm.refresh());
+          setTimeout(refreshOnViewNow, 0, cm);
         }
       }
     }
   }
 
+  async function refreshOnViewNow(cm, code) {
+    cm.refresh();
+    linter.enableForEditor(cm, code);
+  }
+
   function toggleContextMenuDelete(event) {
     if (chrome.contextMenus && event.button === 2 && prefs.get('editor.contextDelete')) {
       chrome.contextMenus.update('editor.contextDelete', {
diff --git a/edit/source-editor.js b/edit/source-editor.js
index c2b1cd93..b262bbdc 100644
--- a/edit/source-editor.js
+++ b/edit/source-editor.js
@@ -91,6 +91,7 @@ function SourceEditor() {
     linter.run();
     updateLinterSwitch();
   });
+  setTimeout(linter.enableForEditor, 0, cm);
   if (!$.isTextInput(document.activeElement)) {
     cm.focus();
   }