--- a/toolkit/components/extensions/Extension.jsm
+++ b/toolkit/components/extensions/Extension.jsm
@@ -1709,14 +1709,13 @@ this.Langpack = class extends ExtensionD
         } else {
           // If the path is not a string, it's an object with path per platform
           // where the keys are taken from AppConstants.platform
           const platform = AppConstants.platform;
           if (platform in path) {
             chromeEntries.push(["locale", alias, language, path[platform]]);
           }
         }
-
       }
     }
     return chromeEntries;
   }
 };

--- a/toolkit/components/extensions/ExtensionCommon.jsm
+++ b/toolkit/components/extensions/ExtensionCommon.jsm
@@ -18,17 +18,16 @@ this.EXPORTED_SYMBOLS = ["ExtensionCommo
 Cu.importGlobalProperties(["fetch"]);
 
 Cu.import("resource://gre/modules/Services.jsm");
 Cu.import("resource://gre/modules/XPCOMUtils.jsm");
 
 XPCOMUtils.defineLazyModuleGetters(this, {
   ConsoleAPI: "resource://gre/modules/Console.jsm",
   MessageChannel: "resource://gre/modules/MessageChannel.jsm",
-  Preferences: "resource://gre/modules/Preferences.jsm",
   PrivateBrowsingUtils: "resource://gre/modules/PrivateBrowsingUtils.jsm",
   Schemas: "resource://gre/modules/Schemas.jsm",
 });
 
 XPCOMUtils.defineLazyServiceGetter(this, "styleSheetService",
                                    "@mozilla.org/content/style-sheet-service;1",
                                    "nsIStyleSheetService");
 
@@ -1499,17 +1498,17 @@ LocaleData.prototype = {
       result.set(key.toLowerCase(), value);
     }
 
     this.messages.set(locale, result);
     return result;
   },
 
   get acceptLanguages() {
-    let result = Preferences.get("intl.accept_languages", "", Ci.nsIPrefLocalizedString);
+    let result = Services.prefs.getComplexValue("intl.accept_languages", Ci.nsIPrefLocalizedString).data;
     return result.split(/\s*,\s*/g);
   },
 
 
   get uiLocale() {
     return Services.locale.getAppLocaleAsBCP47();
   },
 };

--- a/toolkit/components/extensions/ExtensionUtils.jsm
+++ b/toolkit/components/extensions/ExtensionUtils.jsm
@@ -1,20 +1,17 @@
 /* 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/. */
 
 "use strict";
 
 this.EXPORTED_SYMBOLS = ["ExtensionUtils"];
 
-const Ci = Components.interfaces;
-const Cc = Components.classes;
-const Cu = Components.utils;
-const Cr = Components.results;
+const {classes: Cc, interfaces: Ci, utils: Cu, results: Cr} = Components;
 
 Cu.import("resource://gre/modules/Services.jsm");
 Cu.import("resource://gre/modules/XPCOMUtils.jsm");
 
 XPCOMUtils.defineLazyModuleGetter(this, "ConsoleAPI",
                                   "resource://gre/modules/Console.jsm");
 XPCOMUtils.defineLazyModuleGetter(this, "OS",
                                   "resource://gre/modules/osfile.jsm");
@@ -297,19 +294,17 @@ function promiseDocumentReady(doc) {
  * @returns {Promise<Document>}
  */
 function promiseDocumentLoaded(doc) {
   if (doc.readyState == "complete") {
     return Promise.resolve(doc);
   }
 
   return new Promise(resolve => {
-    doc.defaultView.addEventListener("load", function(event) {
-      resolve(doc);
-    }, {once: true});
+    doc.defaultView.addEventListener("load", () => resolve(doc), {once: true});
   });
 }
 
 /**
  * Returns a Promise which resolves when the given event is dispatched to the
  * given element.
  *
  * @param {Element} element

--- a/toolkit/components/extensions/MessageChannel.jsm
+++ b/toolkit/components/extensions/MessageChannel.jsm
@@ -95,20 +95,17 @@
  *  },
  *
  */
 
 this.EXPORTED_SYMBOLS = ["MessageChannel"];
 
 /* globals MessageChannel */
 
-const Ci = Components.interfaces;
-const Cc = Components.classes;
-const Cu = Components.utils;
-const Cr = Components.results;
+const {classes: Cc, interfaces: Ci, utils: Cu, results: Cr} = Components;
 
 Cu.import("resource://gre/modules/AppConstants.jsm");
 Cu.import("resource://gre/modules/ExtensionUtils.jsm");
 Cu.import("resource://gre/modules/Services.jsm");
 
 const {
   MessageManagerProxy,
 } = ExtensionUtils;