--- a/browser/components/preferences/in-content/main.js
+++ b/browser/components/preferences/in-content/main.js
@@ -1,21 +1,16 @@
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this file,
  * You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 /* import-globals-from preferences.js */
 /* import-globals-from ../../../../toolkit/mozapps/preferences/fontbuilder.js */
 /* import-globals-from ../../../base/content/aboutDialog-appUpdater.js */
 
-XPCOMUtils.defineLazyModuleGetter(this, "ExtensionSettingsStore",
-                                  "resource://gre/modules/ExtensionSettingsStore.jsm");
-XPCOMUtils.defineLazyModuleGetter(this, "AddonManager",
-                                  "resource://gre/modules/AddonManager.jsm");
-
 Components.utils.import("resource://gre/modules/Services.jsm");
 Components.utils.import("resource://gre/modules/Downloads.jsm");
 Components.utils.import("resource://gre/modules/FileUtils.jsm");
 Components.utils.import("resource:///modules/ShellService.jsm");
 Components.utils.import("resource:///modules/TransientPrefs.jsm");
 Components.utils.import("resource://gre/modules/Services.jsm");
 Components.utils.import("resource://gre/modules/AppConstants.jsm");
 Components.utils.import("resource://gre/modules/DownloadUtils.jsm");
@@ -255,21 +250,21 @@ var gMainPane = {
     }
     setEventListener("useCurrent", "command",
       gMainPane.setHomePageToCurrent);
     setEventListener("useBookmark", "command",
       gMainPane.setHomePageToBookmark);
     setEventListener("restoreDefaultHomePage", "command",
       gMainPane.restoreDefaultHomePage);
     setEventListener("disableHomePageExtension", "command",
-                     gMainPane.makeDisableControllingExtension("prefs", "homepage_override"));
+                     makeDisableControllingExtension("prefs", "homepage_override"));
     setEventListener("disableContainersExtension", "command",
-                     gMainPane.makeDisableControllingExtension("prefs", "privacy.containers"));
+                     makeDisableControllingExtension("prefs", "privacy.containers"));
     setEventListener("disableNewTabExtension", "command",
-                     gMainPane.makeDisableControllingExtension("url_overrides", "newTabURL"));
+                     makeDisableControllingExtension("url_overrides", "newTabURL"));
     setEventListener("chooseLanguage", "command",
       gMainPane.showLanguages);
     setEventListener("translationAttributionImage", "click",
       gMainPane.openTranslationProviderAttribution);
     setEventListener("translateButton", "command",
       gMainPane.showTranslationExceptions);
     setEventListener("font.language.group", "change",
       gMainPane._rebuildFonts);
@@ -769,17 +764,17 @@ var gMainPane = {
     let tabs = this._getTabsForHomePage();
 
     if (tabs.length > 1)
       useCurrent.label = useCurrent.getAttribute("label2");
     else
       useCurrent.label = useCurrent.getAttribute("label1");
 
     // If the homepage is controlled by an extension then you can't use this.
-    if (await getControllingExtensionId("prefs", "homepage_override")) {
+    if (await getControllingExtensionInfo("prefs", "homepage_override")) {
       useCurrent.disabled = true;
       return;
     }
 
     // In this case, the button's disabled state is set by preferences.xml.
     let prefName = "pref.browser.homepage.disable_button.current_page";
     if (document.getElementById(prefName).locked)
       return;
@@ -817,24 +812,16 @@ var gMainPane = {
   /**
    * Restores the default home page as the user's home page.
    */
   restoreDefaultHomePage() {
     var homePage = document.getElementById("browser.startup.homepage");
     homePage.value = homePage.defaultValue;
   },
 
-  makeDisableControllingExtension(type, settingName) {
-    return async function disableExtension() {
-      let id = await getControllingExtensionId(type, settingName);
-      let addon = await AddonManager.getAddonByID(id);
-      addon.userDisabled = true;
-    };
-  },
-
   /**
    * Utility function to enable/disable the button specified by aButtonID based
    * on the value of the Boolean preference specified by aPreferenceID.
    */
   updateButtons(aButtonID, aPreferenceID) {
     var button = document.getElementById(aButtonID);
     var preference = document.getElementById(aPreferenceID);
     button.disabled = preference.value != true;
@@ -2655,79 +2642,16 @@ function getLocalHandlerApp(aFile) {
   var localHandlerApp = Cc["@mozilla.org/uriloader/local-handler-app;1"].
     createInstance(Ci.nsILocalHandlerApp);
   localHandlerApp.name = getFileDisplayName(aFile);
   localHandlerApp.executable = aFile;
 
   return localHandlerApp;
 }
 
-let extensionControlledContentIds = {
-  "privacy.containers": "browserContainersExtensionContent",
-  "homepage_override": "browserHomePageExtensionContent",
-  "newTabURL": "browserNewTabExtensionContent",
-};
-
-/**
-  * Check if a pref is being managed by an extension.
-  */
-async function getControllingExtensionId(type, settingName) {
-  await ExtensionSettingsStore.initialize();
-  return ExtensionSettingsStore.getTopExtensionId(type, settingName);
-}
-
-function getControllingExtensionEl(settingName) {
-  return document.getElementById(extensionControlledContentIds[settingName]);
-}
-
-async function handleControllingExtension(type, settingName) {
-  let controllingExtensionId = await getControllingExtensionId(type, settingName);
-
-  if (controllingExtensionId) {
-    showControllingExtension(settingName, controllingExtensionId);
-  } else {
-    hideControllingExtension(settingName);
-  }
-
-  return !!controllingExtensionId;
-}
-
-async function showControllingExtension(settingName, extensionId) {
-  let extensionControlledContent = getControllingExtensionEl(settingName);
-  // Tell the user what extension is controlling the setting.
-  let addon = await AddonManager.getAddonByID(extensionId);
-  const defaultIcon = "chrome://mozapps/skin/extensions/extensionGeneric.svg";
-  let stringParts = document
-    .getElementById("bundlePreferences")
-    .getString(`extensionControlled.${settingName}`)
-    .split("%S");
-  let description = extensionControlledContent.querySelector("description");
-
-  // Remove the old content from the description.
-  while (description.firstChild) {
-    description.firstChild.remove();
-  }
-
-  // Populate the description.
-  description.appendChild(document.createTextNode(stringParts[0]));
-  let image = document.createElement("image");
-  image.setAttribute("src", addon.iconURL || defaultIcon);
-  image.classList.add("extension-controlled-icon");
-  description.appendChild(image);
-  description.appendChild(document.createTextNode(` ${addon.name}`));
-  description.appendChild(document.createTextNode(stringParts[1]));
-
-  // Show the controlling extension row and hide the old label.
-  extensionControlledContent.hidden = false;
-}
-
-function hideControllingExtension(settingName) {
-  getControllingExtensionEl(settingName).hidden = true;
-}
-
 /**
  * An enumeration of items in a JS array.
  *
  * FIXME: use ArrayConverter once it lands (bug 380839).
  *
  * @constructor
  */
 function ArrayEnumerator(aItems) {

--- a/browser/components/preferences/in-content/preferences.js
+++ b/browser/components/preferences/in-content/preferences.js
@@ -18,16 +18,21 @@ var Cc = Components.classes;
 var Ci = Components.interfaces;
 var Cu = Components.utils;
 var Cr = Components.results;
 
 Cu.import("resource://gre/modules/XPCOMUtils.jsm");
 Cu.import("resource://gre/modules/Services.jsm");
 Cu.import("resource://gre/modules/AppConstants.jsm");
 
+XPCOMUtils.defineLazyModuleGetter(this, "ExtensionSettingsStore",
+                                  "resource://gre/modules/ExtensionSettingsStore.jsm");
+XPCOMUtils.defineLazyModuleGetter(this, "AddonManager",
+                                  "resource://gre/modules/AddonManager.jsm");
+
 var gLastHash = "";
 
 var gCategoryInits = new Map();
 function init_category_if_required(category) {
   let categoryInfo = gCategoryInits.get(category);
   if (!categoryInfo) {
     throw "Unknown in-content prefs category! Can't init " + category;
   }
@@ -352,8 +357,82 @@ function confirmRestartPrompt(aRestartTo
 function appendSearchKeywords(aId, keywords) {
   let element = document.getElementById(aId);
   let searchKeywords = element.getAttribute("searchkeywords");
   if (searchKeywords) {
     keywords.push(searchKeywords);
   }
   element.setAttribute("searchkeywords", keywords.join(" "));
 }
+
+let extensionControlledContentIds = {
+  "privacy.containers": "browserContainersExtensionContent",
+  "homepage_override": "browserHomePageExtensionContent",
+  "newTabURL": "browserNewTabExtensionContent",
+  "defaultSearch": "browserDefaultSearchExtensionContent",
+};
+
+/**
+  * Check if a pref is being managed by an extension.
+  */
+async function getControllingExtensionInfo(type, settingName) {
+  await ExtensionSettingsStore.initialize();
+  return ExtensionSettingsStore.getSetting(type, settingName);
+}
+
+function getControllingExtensionEl(settingName) {
+  return document.getElementById(extensionControlledContentIds[settingName]);
+}
+
+async function handleControllingExtension(type, settingName, {filter} = {}) {
+  let info = await getControllingExtensionInfo(type, settingName);
+  filter = filter || (() => true);
+  let isControlled = info && !!info.id && filter(info.value);
+
+  if (isControlled) {
+    showControllingExtension(settingName, info.id);
+  } else {
+    hideControllingExtension(settingName);
+  }
+
+  return isControlled;
+}
+
+async function showControllingExtension(settingName, extensionId) {
+  let extensionControlledContent = getControllingExtensionEl(settingName);
+  // Tell the user what extension is controlling the setting.
+  let addon = await AddonManager.getAddonByID(extensionId);
+  const defaultIcon = "chrome://mozapps/skin/extensions/extensionGeneric.svg";
+  let stringParts = document
+    .getElementById("bundlePreferences")
+    .getString(`extensionControlled.${settingName}`)
+    .split("%S");
+  let description = extensionControlledContent.querySelector("description");
+
+  // Remove the old content from the description.
+  while (description.firstChild) {
+    description.firstChild.remove();
+  }
+
+  // Populate the description.
+  description.appendChild(document.createTextNode(stringParts[0]));
+  let image = document.createElement("image");
+  image.setAttribute("src", addon.iconURL || defaultIcon);
+  image.classList.add("extension-controlled-icon");
+  description.appendChild(image);
+  description.appendChild(document.createTextNode(` ${addon.name}`));
+  description.appendChild(document.createTextNode(stringParts[1]));
+
+  // Show the controlling extension row and hide the old label.
+  extensionControlledContent.hidden = false;
+}
+
+function hideControllingExtension(settingName) {
+  getControllingExtensionEl(settingName).hidden = true;
+}
+
+function makeDisableControllingExtension(type, settingName) {
+  return async function disableExtension() {
+    let {id} = await getControllingExtensionInfo(type, settingName);
+    let addon = await AddonManager.getAddonByID(id);
+    addon.userDisabled = true;
+  };
+}

--- a/browser/components/preferences/in-content/search.js
+++ b/browser/components/preferences/in-content/search.js
@@ -2,19 +2,29 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 /* import-globals-from preferences.js */
 
 Components.utils.import("resource://gre/modules/XPCOMUtils.jsm");
 XPCOMUtils.defineLazyModuleGetter(this, "PlacesUtils",
                                   "resource://gre/modules/PlacesUtils.jsm");
+XPCOMUtils.defineLazyModuleGetter(this, "AddonManager",
+                                  "resource://gre/modules/AddonManager.jsm");
+XPCOMUtils.defineLazyModuleGetter(this, "ExtensionSettingsStore",
+                                  "resource://gre/modules/ExtensionSettingsStore.jsm");
 
 const ENGINE_FLAVOR = "text/x-moz-search-engine";
 
+function handleControllingDefaultSearchExtension() {
+  return handleControllingExtension("default_search", "defaultSearch", {
+    filter: (value) => value == Services.search.currentEngine.name,
+  });
+}
+
 var gEngineView = null;
 
 var gSearchPane = {
 
   /**
    * Initialize autocomplete to ensure prefs are in sync.
    */
   _initAutocomplete() {
@@ -92,16 +102,28 @@ var gSearchPane = {
       item.setAttribute("class", "menuitem-iconic searchengine-menuitem menuitem-with-favicon");
       if (e.iconURI) {
         item.setAttribute("image", e.iconURI.spec);
       }
       item.engine = e;
       if (e.name == currentEngine)
         list.selectedItem = item;
     });
+
+
+    handleControllingDefaultSearchExtension();
+    let searchEngineListener = {
+      observe(subject, topic, data) {
+        handleControllingDefaultSearchExtension();
+      },
+    };
+    Services.obs.addObserver(searchEngineListener, "browser-search-engine-modified");
+    window.addEventListener("unload", () => {
+      Services.obs.removeObserver(searchEngineListener, "browser-search-engine-modified");
+    });
   },
 
   handleEvent(aEvent) {
     switch (aEvent.type) {
       case "click":
         if (aEvent.target.id != "engineChildren" &&
             !aEvent.target.classList.contains("searchEngineAction")) {
           let engineList = document.getElementById("engineList");

--- a/browser/components/preferences/in-content/search.xul
+++ b/browser/components/preferences/in-content/search.xul
@@ -39,24 +39,30 @@
         <image class="searchBarImage searchBarShownImage" role="presentation"/>
       </radiogroup>
     </groupbox>
 
     <!-- Default Search Engine -->
     <groupbox id="defaultEngineGroup" data-category="paneSearch">
       <caption><label>&defaultSearchEngine.label;</label></caption>
       <description>&chooseYourDefaultSearchEngine2.label;</description>
+
+      <hbox id="browserDefaultSearchExtensionContent" align="center" hidden="true">
+        <description control="disableDefaultSearchExtension" flex="1"/>
+      </hbox>
+
       <hbox>
         <!-- Please don't remove the wrapping hbox/vbox/box for these elements. It's used to properly compute the search tooltip position. -->
         <hbox>
           <menulist id="defaultEngine">
             <menupopup/>
           </menulist>
         </hbox>
       </hbox>
+
       <checkbox id="suggestionsInSearchFieldsCheckbox"
                 label="&provideSearchSuggestions.label;"
                 accesskey="&provideSearchSuggestions.accesskey;"
                 preference="browser.search.suggest.enabled"/>
       <vbox class="indent">
         <checkbox id="urlBarSuggestion" label="&showURLBarSuggestions2.label;"
                   accesskey="&showURLBarSuggestions2.accesskey;"
                   preference="browser.urlbar.suggest.searches"/>

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--- a/browser/components/preferences/in-content/tests/browser.ini
+++ b/browser/components/preferences/in-content/tests/browser.ini
@@ -1,13 +1,14 @@
 [DEFAULT]
 support-files =
   head.js
   privacypane_tests_perwindow.js
   site_data_test.html
+  addons/set_default_search.xpi
   addons/set_homepage.xpi
   addons/set_newtab.xpi
   offline/offline.html
   offline/manifest.appcache
 
 [browser_applications_selection.js]
 skip-if = os == 'linux' # bug 1382057
 [browser_advanced_update.js]

--- a/browser/components/preferences/in-content/tests/browser_extension_controlled.js
+++ b/browser/components/preferences/in-content/tests/browser_extension_controlled.js
@@ -119,13 +119,50 @@ add_task(async function testExtensionCon
   is(controlledContent.hidden, false, "The extension controlled row is hidden");
 
   // Disable the extension.
   doc.getElementById("disableNewTabExtension").click();
 
   await waitForMessageHidden("browserNewTabExtensionContent");
 
   ok(!aboutNewTabService.newTabURL.startsWith("moz-extension:"), "new tab page is set back to default");
+  is(controlledContent.hidden, true, "The extension controlled row is shown");
+
+  await BrowserTestUtils.removeTab(gBrowser.selectedTab);
+});
+
+add_task(async function testExtensionControlledDefaultSearch() {
+  await openPreferencesViaOpenPreferencesAPI("paneSearch", {leaveOpen: true});
+  let doc = gBrowser.contentDocument;
+  is(gBrowser.currentURI.spec, "about:preferences#search",
+     "#search should be in the URI for about:preferences");
+
+  let controlledContent = doc.getElementById("browserDefaultSearchExtensionContent");
+  let initialEngine = Services.search.currentEngine;
+
+  // Ensure the controlled content is hidden when not controlled.
+  is(controlledContent.hidden, true, "The extension controlled row is hidden");
+
+  // Install an extension that will set the default search engine.
+  await installAddon("set_default_search.xpi");
+
+  await waitForMessageShown("browserDefaultSearchExtensionContent");
+
+  // The default search engine has been set by the extension and the user is notified.
+  let controlledLabel = controlledContent.querySelector("description");
+  ok(initialEngine != Services.search.currentEngine, "The default engine has changed.");
+  // There are two spaces before "set_default_search" because it's " <image /> set_default_search".
+  is(controlledLabel.textContent,
+     "An extension,  set_default_search, has set your default search engine.",
+     "The user is notified that an extension is controlling the default search engine");
+  is(controlledContent.hidden, false, "The extension controlled row is shown");
+
+  Services.search.currentEngine = initialEngine;
+
+  await waitForMessageHidden("browserDefaultSearchExtensionContent");
+
+  is(initialEngine, Services.search.currentEngine,
+     "default search engine is set back to default");
   is(controlledContent.hidden, true, "The extension controlled row is hidden");
 
   await BrowserTestUtils.removeTab(gBrowser.selectedTab);
 });
 

--- a/browser/locales/en-US/chrome/browser/preferences/preferences.properties
+++ b/browser/locales/en-US/chrome/browser/preferences/preferences.properties
@@ -281,12 +281,17 @@ defaultContentProcessCount=%S (default)
 # LOCALIZATION NOTE (extensionControlled.homepage_override):
 # This string is shown to notify the user that their home page is being controlled by an extension.
 extensionControlled.homepage_override = An extension, %S, controls your home page.
 
 # LOCALIZATION NOTE (extensionControlled.newTabURL):
 # This string is shown to notify the user that their new tab page is being controlled by an extension.
 extensionControlled.newTabURL = An extension, %S, controls your New Tab page.
 
+# LOCALIZATION NOTE (extensionControlled.defaultSearch):
+# This string is shown to notify the user that the default search engine is being controlled
+# by an extension. %S is the icon and name of the extension.
+extensionControlled.defaultSearch = An extension, %S, has set your default search engine.
+
 # LOCALIZATION NOTE (extensionControlled.privacy.containers):
 # This string is shown to notify the user that Container Tabs are being enabled by an extension
 # %S is the container addon controlling it
 extensionControlled.privacy.containers = An extension, %S, requires Container Tabs.

--- a/toolkit/components/extensions/ExtensionPreferencesManager.jsm
+++ b/toolkit/components/extensions/ExtensionPreferencesManager.jsm
@@ -164,29 +164,16 @@ this.ExtensionPreferencesManager = {
    *
    * @returns {string|number|boolean} The default value of the preference.
    */
   getDefaultValue(prefName) {
     return defaultPreferences.get(prefName);
   },
 
   /**
-   * Gets the id of the extension controlling a preference or null if it isn't
-   * being controlled.
-   *
-   * @param {string} prefName The name of the preference.
-   *
-   * @returns {Promise} Resolves to the id of the extension, or null.
-   */
-  async getControllingExtensionId(prefName) {
-    await ExtensionSettingsStore.initialize();
-    return ExtensionSettingsStore.getTopExtensionId(STORE_TYPE, prefName);
-  },
-
-  /**
    * Indicates that an extension would like to change the value of a previously
    * defined setting.
    *
    * @param {Extension} extension
    *        The extension for which a setting is being set.
    * @param {string} name
    *        The unique id of the setting.
    * @param {any} value

--- a/toolkit/components/extensions/ExtensionSettingsStore.jsm
+++ b/toolkit/components/extensions/ExtensionSettingsStore.jsm
@@ -447,26 +447,16 @@ this.ExtensionSettingsStore = {
     }
 
     let addon = await AddonManager.getAddonByID(id);
     return topItem.installDate > addon.installDate.valueOf() ?
       "controlled_by_other_extensions" :
       "controllable_by_this_extension";
   },
 
-  // Return the id of the controlling extension or null if no extension is
-  // controlling this setting.
-  getTopExtensionId(type, key) {
-    let item = getTopItem(type, key);
-    if (item) {
-      return item.id;
-    }
-    return null;
-  },
-
   /**
    * Test-only method to force reloading of the JSON file.
    *
    * Note that this method simply clears the local variable that stores the
    * file, so the next time the file is accessed it will be reloaded.
    *
    * @returns {Promise}
    *          A promise that resolves once the settings store has been cleared.