diff --git a/install-usercss.html b/install-usercss.html
index 9ed75523..98cd0eec 100644
--- a/install-usercss.html
+++ b/install-usercss.html
@@ -35,6 +35,9 @@
         <div class="actions">
           <h2 class="installed" i18n-text="installButtonInstalled"></h2>
           <button class="install" i18n-text="installButton"></button>
+          <a class="configure-usercss" i18n-title="configureStyle" tabindex="0">
+            <svg class="svg-icon config"><use xlink:href="#svg-icon-config"></use></svg>
+          </a>
           <p id="live-reload-install-hint" hidden></p>
           <label class="set-update-url">
             <input type="checkbox">
@@ -74,6 +77,12 @@
     <symbol id="svg-icon-checked" viewBox="0 0 1000 1000">
       <path fill-rule="evenodd" d="M983.2,184.3L853,69.8c-4-3.5-9.3-5.3-14.5-5c-5.3,0.4-10.3,2.8-13.8,6.8L352.3,609.2L184.4,386.9c-3.2-4.2-8-7-13.2-7.8c-5.3-0.8-10.6,0.6-14.9,3.9L18,487.5c-8.8,6.7-10.6,19.3-3.9,28.1L325,927.2c3.6,4.8,9.3,7.7,15.3,8c0.2,0,0.5,0,0.7,0c5.8,0,11.3-2.5,15.1-6.8L985,212.6C992.3,204.3,991.5,191.6,983.2,184.3z"/>
     </symbol>
+    <symbol id="svg-icon-select-arrow" viewBox="0 0 1792 1792">
+      <path fill-rule="evenodd" d="M1408 704q0 26-19 45l-448 448q-19 19-45 19t-45-19l-448-448q-19-19-19-45t19-45 45-19h896q26 0 45 19t19 45z"/>
+    </symbol>
+    <symbol id="svg-icon-config" viewBox="0 0 16 16">
+      <path d="M13.3,12.8l1.5-2.6l-2.2-1.5c0-0.2,0.1-0.5,0.1-0.7c0-0.2,0-0.5-0.1-0.7l2.2-1.5l-1.5-2.6l-2.4,1.2 c-0.4-0.3-0.8-0.5-1.2-0.7L9.5,1h-3L6.3,3.7C5.9,3.8,5.5,4.1,5.1,4.4L2.7,3.2L1.2,5.8l2.2,1.5c0,0.2-0.1,0.5-0.1,0.7 c0,0.2,0,0.5,0.1,0.7l-2.2,1.5l1.5,2.6l2.4-1.2c0.4,0.3,0.8,0.5,1.2,0.7L6.5,15h3l0.2-2.7c0.4-0.2,0.8-0.4,1.2-0.7L13.3,12.8z  M8,10.3c-1.3,0-2.3-1-2.3-2.3c0-1.3,1-2.3,2.3-2.3c1.3,0,2.3,1,2.3,2.3C10.3,9.3,9.3,10.3,8,10.3z"/>
+    </symbol>
   </svg>
 
   <script src="js/dlg/message-box.js"></script>
diff --git a/install-usercss/install-usercss.css b/install-usercss/install-usercss.css
index 55c2ad90..efc088e3 100644
--- a/install-usercss/install-usercss.css
+++ b/install-usercss/install-usercss.css
@@ -305,6 +305,20 @@ label {
   animation: none;
 }
 
+.configure-usercss .svg-icon.config {
+  width: 20px;
+  height: 20px;
+  margin-top: -3px;
+}
+#message-box.config-dialog {
+  width: 0;
+  height: 0;
+  background: none;
+}
+#message-box.config-dialog > div {
+  box-shadow: 5px 5px 50px rgba(0, 0, 0, 0.75); /* copied from message-box.css + darkened the color */
+}
+
 /************ reponsive layouts ************/
 
 @media (max-width: 850px) {
@@ -417,6 +431,10 @@ label {
     flex-shrink: 0;
     margin-right: 1em;
   }
+  #message-box.config-dialog > div {
+    top: auto;
+    bottom: 3rem;
+  }
 }
 
 /* Retina-specific stuff here */
diff --git a/install-usercss/install-usercss.js b/install-usercss/install-usercss.js
index 74ad9388..6645e882 100644
--- a/install-usercss/install-usercss.js
+++ b/install-usercss/install-usercss.js
@@ -1,6 +1,6 @@
-/* global $ $create $createLink $$remove */
+/* global $ $create $createLink $$remove showSpinner */// dom.js
 /* global API */// msg.js
-/* global closeCurrentTab */// toolbox.js
+/* global closeCurrentTab deepEqual */// toolbox.js
 /* global messageBox */
 /* global prefs */
 /* global preinit */
@@ -13,20 +13,16 @@ let installed;
 let installedDup;
 let liveReload;
 let tabId;
+let vars;
 
 // "History back" in Firefox (for now) restores the old DOM including the messagebox,
 // which stays after installing since we don't want to wait for the fadeout animation before resolving.
 document.on('visibilitychange', () => {
-  if (messageBox.element) messageBox.element.remove();
+  $$remove('#message-box:not(.config-dialog)');
   if (installed) liveReload.onToggled();
 });
 
-setTimeout(() => {
-  if (!cm) {
-    $('#header').appendChild($create('.lds-spinner',
-      new Array(12).fill($create('div')).map(e => e.cloneNode())));
-  }
-}, 200);
+setTimeout(() => !cm && showSpinner($('#header')), 200);
 
 /*
  * Preinit starts to download as early as possible,
@@ -187,11 +183,29 @@ function updateMeta(style, dup = installedDup) {
     $('.external-link').appendChild(externalLink);
   }
 
+  Object.assign($('.configure-usercss'), {
+    hidden: !data.vars,
+    onclick: openConfigDialog,
+  });
+  if (!data.vars) {
+    $$remove('#message-box.config-dialog');
+  } else if (!deepEqual(data.vars, vars)) {
+    vars = data.vars;
+    // Use the user-customized vars from the installed style
+    for (const [dk, dv] of Object.entries(dup && dupData.vars || {})) {
+      const v = vars[dk];
+      if (v && v.type === dv.type) {
+        v.value = dv.value;
+      }
+    }
+    openConfigDialog();
+  }
+
   $('#header').dataset.arrivedFast = performance.now() < 500;
   $('#header').classList.add('meta-init');
   $('#header').classList.remove('meta-init-error');
-  setTimeout(() => $$remove('.lds-spinner'), 1000);
 
+  setTimeout(() => $$remove('.lds-spinner'), 1000);
   showError('');
   requestAnimationFrame(adjustCodeHeight);
 
@@ -233,6 +247,11 @@ function updateMeta(style, dup = installedDup) {
         )),
       ]));
   }
+
+  async function openConfigDialog() {
+    await require(['/js/dlg/config-dialog']); /* global configDialog */
+    configDialog(style);
+  }
 }
 
 function showError(err) {
diff --git a/js/dlg/config-dialog.css b/js/dlg/config-dialog.css
index e6fe339c..7464e30c 100644
--- a/js/dlg/config-dialog.css
+++ b/js/dlg/config-dialog.css
@@ -2,12 +2,12 @@
   --onoffswitch-width: 60px;
 }
 
-#stylus-manage .config-dialog #message-box-contents {
-  padding: 2em 16px;
+.config-dialog {
+  --pad: 16px;
 }
 
-#stylus-popup .config-dialog #message-box-contents {
-  padding: 8px 16px;
+.config-dialog #message-box-contents {
+  padding: var(--pad);
 }
 
 #stylus-popup .config-dialog > div {
@@ -33,7 +33,7 @@
   display: flex;
   padding: .75em 0;
   align-items: center;
-  margin-right: -16px; /* for .config-reset-icon */
+  margin-right: calc(-1 * var(--pad)); /* for .config-reset-icon */
 }
 
 .config-body .select-resizer {
@@ -120,14 +120,14 @@
 }
 
 .config-reset-icon {
-  height: 16px;
+  height: var(--pad);
 }
 
 .config-reset-icon .svg-icon {
   cursor: pointer;
   fill: #aaa;
-  width: 16px;
-  height: 16px;
+  width: var(--pad);
+  height: var(--pad);
   padding: 0 1px;
   box-sizing: border-box;
   flex-shrink: 0;
@@ -139,7 +139,7 @@
 
 #config-autosave-wrapper {
   position: relative;
-  padding: 0 0 0 16px;
+  padding: 0 0 0 var(--pad);
   display: inline-flex;
 }
 
diff --git a/js/dlg/config-dialog.js b/js/dlg/config-dialog.js
index c1054299..9e539301 100644
--- a/js/dlg/config-dialog.js
+++ b/js/dlg/config-dialog.js
@@ -28,8 +28,9 @@ async function configDialog(style) {
   let varsInitial = getInitialValues(varsHash);
 
   const elements = [];
-  const colorpicker = window.colorpicker();
-  const isPopup = location.href.includes('popup.html');
+  const isInstaller = location.pathname.startsWith('/install-usercss.html');
+  const isPopup = location.pathname.startsWith('/popup.html');
+  const colorpicker = ((window.CodeMirror || {}).prototype || window).colorpicker();
   const buttons = {};
 
   buildConfigForm();
@@ -122,7 +123,7 @@ async function configDialog(style) {
     buttons.close.textContent = t(someDirty ? 'confirmCancel' : 'confirmClose');
   }
 
-  async function save({anyChangeIsDirty = false} = {}, bgStyle) {
+  async function save({anyChangeIsDirty = false} = {}) {
     for (let delay = 1; saving && delay < 1000; delay *= 2) {
       await new Promise(resolve => setTimeout(resolve, delay));
     }
@@ -132,15 +133,13 @@ async function configDialog(style) {
     if (!vars.some(va => va.dirty || anyChangeIsDirty && va.value !== va.savedValue)) {
       return;
     }
-    if (!bgStyle) {
-      bgStyle = await API.styles.get(style.id).catch(() => ({}));
-    }
+    const bgStyle = !isInstaller && await API.styles.get(style.id).catch(() => ({}));
     style = style.sections ? Object.assign({}, style) : style;
     style.enabled = true;
     style.sourceCode = null;
     style.sections = null;
     const styleVars = style.usercssData.vars;
-    const bgVars = (bgStyle.usercssData || {}).vars || {};
+    const bgVars = isInstaller ? styleVars : (bgStyle.usercssData || {}).vars || {};
     const invalid = [];
     let numValid = 0;
     for (const va of vars) {
@@ -184,7 +183,7 @@ async function configDialog(style) {
     }
     saving = true;
     try {
-      const newVars = await API.usercss.configVars(style.id, style.usercssData.vars);
+      const newVars = isInstaller ? styleVars : await API.usercss.configVars(style.id, styleVars);
       varsInitial = getInitialValues(newVars);
       vars.forEach(va => onchange({target: va.input, justSaved: true}));
       renderValues();
diff --git a/js/dlg/message-box.js b/js/dlg/message-box.js
index 3c348882..31de0726 100644
--- a/js/dlg/message-box.js
+++ b/js/dlg/message-box.js
@@ -40,10 +40,9 @@ messageBox.show = async ({
 }) => {
   await require(['/js/dlg/message-box.css']);
   if (!messageBox.listeners) initOwnListeners();
-  bindGlobalListeners();
   createElement();
+  bindGlobalListeners();
   document.body.appendChild(messageBox.element);
-  bindElementLiseners();
 
   messageBox._originalFocus = document.activeElement;
   // focus the first focusable child but skip the first external link which is usually `feedback`
@@ -132,15 +131,9 @@ messageBox.show = async ({
         listening = false;
       },
       mouseMove(event) {
-        const x = clamp(event.clientX, 30, innerWidth - 30) - clickX;
-        const y = clamp(event.clientY, 30, innerHeight - 30) - clickY;
-
-        offsetX = x;
-        offsetY = y;
-
-        $('#message-box > div').style.transform =
-          `translateX(${x}px) 
-          translateY(${y}px)`;
+        offsetX = clamp(event.clientX, 30, innerWidth - 30) - clickX;
+        offsetY = clamp(event.clientY, 30, innerHeight - 30) - clickY;
+        messageBox.element.firstChild.style.transform = `translate(${offsetX}px,${offsetY}px)`;
       },
     };
   }
@@ -164,7 +157,7 @@ messageBox.show = async ({
     messageBox.element =
       $create({id, className}, [
         $create([
-          $create(`#${id}-title`, title),
+          $create(`#${id}-title`, {onmousedown: messageBox.listeners.mouseDown}, title),
           $create(`#${id}-close-icon`, {onclick: messageBox.listeners.closeIcon},
             $create('SVG:svg.svg-icon', {viewBox: '0 0 20 20'},
               $create('SVG:path', {d: 'M11.69,10l4.55,4.55-1.69,1.69L10,11.69,' +
@@ -191,16 +184,11 @@ messageBox.show = async ({
     window.on('keydown', messageBox.listeners.key, true);
   }
 
-  function bindElementLiseners() {
-    $('#message-box-title').on('mousedown', messageBox.listeners.mouseDown, {passive: true});
-  }
-
   function unbindGlobalListeners() {
     window.off('keydown', messageBox.listeners.key, true);
     window.off('scroll', messageBox.listeners.scroll);
     window.off('mouseup', messageBox.listeners.mouseUp);
     window.off('mousemove', messageBox.listeners.mouseMove);
-    $('#message-box-title').off('mousedown', messageBox.listeners.mouseDown);
   }
 
   function removeSelf() {