--- a/mobile/android/components/extensions/ext-android.js
+++ b/mobile/android/components/extensions/ext-android.js
@@ -1,16 +1,16 @@
 "use strict";
 
 XPCOMUtils.defineLazyModuleGetter(global, "EventEmitter",
                                   "resource://gre/modules/EventEmitter.jsm");
 
 // This function is pretty tightly tied to Extension.jsm.
 // Its job is to fill in the |tab| property of the sender.
-function getSender(extension, target, sender) {
+const getSender = (extension, target, sender) => {
   let tabId;
   if ("tabId" in sender) {
     // The message came from a privileged extension page running in a tab. In
     // that case, it should include a tabId property (which is filled in by the
     // page-open listener below).
     tabId = sender.tabId;
     delete sender.tabId;
   } else if (target instanceof Ci.nsIDOMXULElement) {
@@ -18,17 +18,17 @@ function getSender(extension, target, se
   }
 
   if (tabId) {
     let tab = extension.tabManager.get(tabId, null);
     if (tab) {
       sender.tab = tab.convert();
     }
   }
-}
+};
 
 // Used by Extension.jsm
 global.tabGetSender = getSender;
 
 /* eslint-disable mozilla/balanced-listeners */
 extensions.on("page-shutdown", (type, context) => {
   if (context.viewType == "tab") {
     if (context.extension.id !== context.xulBrowser.contentPrincipal.addonId) {

--- a/mobile/android/components/extensions/ext-browserAction.js
+++ b/mobile/android/components/extensions/ext-browserAction.js
@@ -8,17 +8,17 @@ XPCOMUtils.defineLazyModuleGetter(this, 
 XPCOMUtils.defineLazyModuleGetter(this, "Services",
                                   "resource://gre/modules/Services.jsm");
 
 // Import the android BrowserActions module.
 XPCOMUtils.defineLazyModuleGetter(this, "BrowserActions",
                                   "resource://gre/modules/BrowserActions.jsm");
 
 // WeakMap[Extension -> BrowserAction]
-var browserActionMap = new WeakMap();
+let browserActionMap = new WeakMap();
 
 class BrowserAction {
   constructor(options, extension) {
     this.uuid = `{${extension.uuid}}`;
 
     this.defaults = {
       name: options.default_title || extension.name,
     };

--- a/mobile/android/components/extensions/ext-pageAction.js
+++ b/mobile/android/components/extensions/ext-pageAction.js
@@ -14,17 +14,17 @@ XPCOMUtils.defineLazyModuleGetter(this, 
 
 Cu.import("resource://gre/modules/ExtensionParent.jsm");
 
 var {
   IconDetails,
 } = ExtensionParent;
 
 // WeakMap[Extension -> PageAction]
-var pageActionMap = new WeakMap();
+let pageActionMap = new WeakMap();
 
 class PageAction {
   constructor(manifest, extension) {
     this.id = null;
 
     this.extension = extension;
 
     this.defaults = {

--- a/mobile/android/components/extensions/ext-tabs.js
+++ b/mobile/android/components/extensions/ext-tabs.js
@@ -10,21 +10,21 @@ XPCOMUtils.defineLazyModuleGetter(this, 
                                   "resource://gre/modules/MatchPattern.jsm");
 XPCOMUtils.defineLazyModuleGetter(this, "PrivateBrowsingUtils",
                                   "resource://gre/modules/PrivateBrowsingUtils.jsm");
 XPCOMUtils.defineLazyModuleGetter(this, "PromiseUtils",
                                   "resource://gre/modules/PromiseUtils.jsm");
 XPCOMUtils.defineLazyModuleGetter(this, "Services",
                                   "resource://gre/modules/Services.jsm");
 
-function getBrowserWindow(window) {
+const getBrowserWindow = window => {
   return window.QueryInterface(Ci.nsIInterfaceRequestor).getInterface(Ci.nsIDocShell)
                .QueryInterface(Ci.nsIDocShellTreeItem).rootTreeItem
                .QueryInterface(Ci.nsIInterfaceRequestor).getInterface(Ci.nsIDOMWindow);
-}
+};
 
 let tabListener = {
   tabReadyInitialized: false,
   tabReadyPromises: new WeakMap(),
   initializingTabs: new WeakSet(),
 
   initTabReady() {
     if (!this.tabReadyInitialized) {