--- a/browser/components/extensions/ext-contextMenus.js
+++ b/browser/components/extensions/ext-contextMenus.js
@@ -1,13 +1,12 @@
 /* -*- Mode: indent-tabs-mode: nil; js-indent-level: 2 -*- */
 /* vim: set sts=2 sw=2 et tw=80: */
 "use strict";
 
-Cu.import("resource://gre/modules/ExtensionManagement.jsm");
 Cu.import("resource://gre/modules/MatchPattern.jsm");
 Cu.import("resource://gre/modules/Services.jsm");
 
 XPCOMUtils.defineLazyModuleGetter(this, "NetUtil",
                                   "resource://gre/modules/NetUtil.jsm");
 
 var {
   ExtensionError,

--- a/browser/components/extensions/test/browser/browser_ext_tabs_executeScript.js
+++ b/browser/components/extensions/test/browser/browser_ext_tabs_executeScript.js
@@ -1,14 +1,16 @@
 /* -*- Mode: indent-tabs-mode: nil; js-indent-level: 2 -*- */
 /* vim: set sts=2 sw=2 et tw=80: */
 "use strict";
 
+XPCOMUtils.defineLazyPreferenceGetter(this, "useRemoteWebExtensions",
+                                      "extensions.webextensions.remote", false);
+
 add_task(async function testExecuteScript() {
-  let {ExtensionManagement} = Cu.import("resource://gre/modules/ExtensionManagement.jsm", {});
   let {MessageChannel} = Cu.import("resource://gre/modules/MessageChannel.jsm", {});
 
   function countMM(messageManagerMap) {
     let count = 0;
     // List of permanent message managers in the main process. We should not
     // count them in the test because MessageChannel unsubscribes when the
     // message manager closes, which never happens to these, of course.
     let globalMMs = [
@@ -252,13 +254,13 @@ add_task(async function testExecuteScrip
 
   await extension.unload();
 
   await BrowserTestUtils.removeTab(tab);
 
   // Make sure that we're not holding on to references to closed message
   // managers.
   is(countMM(MessageChannel.messageManagers), messageManagersSize, "Message manager count");
-  if (!ExtensionManagement.useRemoteWebExtensions) {
+  if (!useRemoteWebExtensions) {
     is(countMM(MessageChannel.responseManagers), responseManagersSize, "Response manager count");
   }
   is(MessageChannel.pendingResponses.size, 0, "Pending response count");
 });

--- a/browser/components/extensions/test/browser/browser_ext_webNavigation_frameId0.js
+++ b/browser/components/extensions/test/browser/browser_ext_webNavigation_frameId0.js
@@ -1,26 +1,13 @@
 /* -*- Mode: indent-tabs-mode: nil; js-indent-level: 2 -*- */
 /* vim: set sts=2 sw=2 et tw=80: */
 "use strict";
 
 add_task(async function webNavigation_getFrameId_of_existing_main_frame() {
-  // Whether the frame ID in the extension API is 0 is determined by a map that
-  // is maintained by |Frames| in ExtensionManagement.jsm. This map is filled
-  // using data from content processes. But if ExtensionManagement.jsm is not
-  // imported, then the "Extension:TopWindowID" message gets lost.
-  // As a result, if the state is not synchronized again, the webNavigation API
-  // will mistakenly report a non-zero frame ID for top-level frames.
-  //
-  // If you want to be absolutely sure that the frame ID is correct, don't open
-  // tabs before starting an extension, or explicitly load the module in the
-  // main process:
-  // Cu.import("resource://gre/modules/ExtensionManagement.jsm", {});
-  //
-  // Or simply run the test again.
   const BASE = "http://mochi.test:8888/browser/browser/components/extensions/test/browser/";
   const DUMMY_URL = BASE + "file_dummy.html";
   let tab = await BrowserTestUtils.openNewForegroundTab(gBrowser, DUMMY_URL, true);
 
   async function background(DUMMY_URL) {
     let tabs = await browser.tabs.query({active: true, currentWindow: true});
     let frames = await browser.webNavigation.getAllFrames({tabId: tabs[0].id});
     browser.test.assertEq(1, frames.length, "The dummy page has one frame");

--- a/browser/components/extensions/test/xpcshell/head.js
+++ b/browser/components/extensions/test/xpcshell/head.js
@@ -7,18 +7,16 @@ const {classes: Cc, interfaces: Ci, util
 Components.utils.import("resource://gre/modules/XPCOMUtils.jsm");
 
 XPCOMUtils.defineLazyModuleGetter(this, "AppConstants",
                                   "resource://gre/modules/AppConstants.jsm");
 XPCOMUtils.defineLazyModuleGetter(this, "Extension",
                                   "resource://gre/modules/Extension.jsm");
 XPCOMUtils.defineLazyModuleGetter(this, "ExtensionData",
                                   "resource://gre/modules/Extension.jsm");
-XPCOMUtils.defineLazyModuleGetter(this, "ExtensionManagement",
-                                  "resource://gre/modules/ExtensionManagement.jsm");
 XPCOMUtils.defineLazyModuleGetter(this, "ExtensionTestUtils",
                                   "resource://testing-common/ExtensionXPCShellUtils.jsm");
 XPCOMUtils.defineLazyModuleGetter(this, "FileUtils",
                                   "resource://gre/modules/FileUtils.jsm");
 XPCOMUtils.defineLazyModuleGetter(this, "HttpServer",
                                   "resource://testing-common/httpd.js");
 XPCOMUtils.defineLazyModuleGetter(this, "NetUtil",
                                   "resource://gre/modules/NetUtil.jsm");

deleted file mode 100644
--- a/toolkit/components/extensions/ExtensionManagement.jsm
+++ /dev/null
@@ -1,38 +0,0 @@
-/* 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";
-
-/* exported ExtensionManagement */
-
-this.EXPORTED_SYMBOLS = ["ExtensionManagement"];
-
-const Ci = Components.interfaces;
-const Cc = Components.classes;
-const Cu = Components.utils;
-const Cr = Components.results;
-
-Cu.import("resource://gre/modules/Services.jsm");
-Cu.import("resource://gre/modules/XPCOMUtils.jsm");
-
-/*
- * This file should be kept short and simple since it's loaded even
- * when no extensions are running.
- */
-
-let cacheInvalidated = 0;
-function onCacheInvalidate() {
-  cacheInvalidated++;
-}
-Services.obs.addObserver(onCacheInvalidate, "startupcache-invalidate");
-
-var ExtensionManagement = {
-  get cacheInvalidated() {
-    return cacheInvalidated;
-  },
-
-  get isExtensionProcess() {
-    return WebExtensionPolicy.isExtensionProcess;
-  },
-};

--- a/toolkit/components/extensions/ExtensionUtils.jsm
+++ b/toolkit/components/extensions/ExtensionUtils.jsm
@@ -17,18 +17,16 @@ Cu.import("resource://gre/modules/Servic
 Cu.import("resource://gre/modules/XPCOMUtils.jsm");
 
 XPCOMUtils.defineLazyModuleGetter(this, "AddonManager",
                                   "resource://gre/modules/AddonManager.jsm");
 XPCOMUtils.defineLazyModuleGetter(this, "AppConstants",
                                   "resource://gre/modules/AppConstants.jsm");
 XPCOMUtils.defineLazyModuleGetter(this, "ConsoleAPI",
                                   "resource://gre/modules/Console.jsm");
-XPCOMUtils.defineLazyModuleGetter(this, "ExtensionManagement",
-                                  "resource://gre/modules/ExtensionManagement.jsm");
 XPCOMUtils.defineLazyModuleGetter(this, "IndexedDB",
                                   "resource://gre/modules/IndexedDB.jsm");
 XPCOMUtils.defineLazyModuleGetter(this, "MessageChannel",
                                   "resource://gre/modules/MessageChannel.jsm");
 XPCOMUtils.defineLazyModuleGetter(this, "Preferences",
                                   "resource://gre/modules/Preferences.jsm");
 XPCOMUtils.defineLazyModuleGetter(this, "Schemas",
                                   "resource://gre/modules/Schemas.jsm");
@@ -57,18 +55,16 @@ let StartupCache = {
   DB_NAME: "ExtensionStartupCache",
 
   SCHEMA_VERSION: 2,
 
   STORE_NAMES: Object.freeze(["locales", "manifests", "schemas"]),
 
   dbPromise: null,
 
-  cacheInvalidated: 0,
-
   initDB(db) {
     for (let name of StartupCache.STORE_NAMES) {
       try {
         db.deleteObjectStore(name);
       } catch (e) {
         // Don't worry if the store doesn't already exist.
       }
       db.createObjectStore(name, {keyPath: "key"});
@@ -89,34 +85,28 @@ let StartupCache = {
 
   async reallyOpen(invalidate = false) {
     if (this.dbPromise) {
       let db = await this.dbPromise;
       db.close();
     }
 
     if (invalidate) {
-      this.cacheInvalidated = ExtensionManagement.cacheInvalidated;
-
       if (Services.appinfo.processType === Services.appinfo.PROCESS_TYPE_DEFAULT) {
         IndexedDB.deleteDatabase(this.DB_NAME, {storage: "persistent"});
       }
     }
 
     return IndexedDB.open(this.DB_NAME,
                           {storage: "persistent", version: this.SCHEMA_VERSION},
                           db => this.initDB(db));
   },
 
   async open() {
-    if (ExtensionManagement.cacheInvalidated > this.cacheInvalidated) {
-      this.dbPromise = this.reallyOpen(true);
-    } else if (!this.dbPromise) {
-      this.dbPromise = this.reallyOpen();
-    }
+    this.dbPromise = this.reallyOpen();
 
     return this.dbPromise;
   },
 
   observe(subject, topic, data) {
     if (topic === "startupcache-invalidate") {
       this.dbPromise = this.reallyOpen(true).catch(e => {});
     }

--- a/toolkit/components/extensions/ext-runtime.js
+++ b/toolkit/components/extensions/ext-runtime.js
@@ -1,18 +1,16 @@
 "use strict";
 
 XPCOMUtils.defineLazyModuleGetter(this, "AddonManager",
                                   "resource://gre/modules/AddonManager.jsm");
 XPCOMUtils.defineLazyModuleGetter(this, "AddonManagerPrivate",
                                   "resource://gre/modules/AddonManager.jsm");
 XPCOMUtils.defineLazyModuleGetter(this, "Extension",
                                   "resource://gre/modules/Extension.jsm");
-XPCOMUtils.defineLazyModuleGetter(this, "ExtensionManagement",
-                                  "resource://gre/modules/ExtensionManagement.jsm");
 XPCOMUtils.defineLazyModuleGetter(this, "NetUtil",
                                   "resource://gre/modules/NetUtil.jsm");
 
 this.runtime = class extends ExtensionAPI {
   getAPI(context) {
     let {extension} = context;
     return {
       runtime: {

--- a/toolkit/components/extensions/ext-webRequest.js
+++ b/toolkit/components/extensions/ext-webRequest.js
@@ -1,12 +1,10 @@
 "use strict";
 
-XPCOMUtils.defineLazyModuleGetter(this, "ExtensionManagement",
-                                  "resource://gre/modules/ExtensionManagement.jsm");
 XPCOMUtils.defineLazyModuleGetter(this, "WebRequest",
                                   "resource://gre/modules/WebRequest.jsm");
 
 // EventManager-like class specifically for WebRequest. Inherits from
 // SingletonEventManager. Takes care of converting |details| parameter
 // when invoking listeners.
 function WebRequestEventManager(context, eventName) {
   let name = `webRequest.${eventName}`;

--- a/toolkit/components/extensions/moz.build
+++ b/toolkit/components/extensions/moz.build
@@ -8,17 +8,16 @@ with Files('**'):
     BUG_COMPONENT = ('Toolkit', 'WebExtensions: General')
 
 EXTRA_JS_MODULES += [
     'Extension.jsm',
     'ExtensionAPI.jsm',
     'ExtensionChild.jsm',
     'ExtensionCommon.jsm',
     'ExtensionContent.jsm',
-    'ExtensionManagement.jsm',
     'ExtensionPageChild.jsm',
     'ExtensionParent.jsm',
     'ExtensionPermissions.jsm',
     'ExtensionPreferencesManager.jsm',
     'ExtensionSettingsStore.jsm',
     'ExtensionStorage.jsm',
     'ExtensionStorageSync.jsm',
     'ExtensionTabs.jsm',

--- a/toolkit/components/extensions/test/xpcshell/head.js
+++ b/toolkit/components/extensions/test/xpcshell/head.js
@@ -10,18 +10,16 @@ Components.utils.import("resource://gre/
 Components.utils.import("resource://testing-common/AddonTestUtils.jsm");
 
 XPCOMUtils.defineLazyModuleGetter(this, "ContentTask",
                                   "resource://testing-common/ContentTask.jsm");
 XPCOMUtils.defineLazyModuleGetter(this, "Extension",
                                   "resource://gre/modules/Extension.jsm");
 XPCOMUtils.defineLazyModuleGetter(this, "ExtensionData",
                                   "resource://gre/modules/Extension.jsm");
-XPCOMUtils.defineLazyModuleGetter(this, "ExtensionManagement",
-                                  "resource://gre/modules/ExtensionManagement.jsm");
 XPCOMUtils.defineLazyModuleGetter(this, "ExtensionTestUtils",
                                   "resource://testing-common/ExtensionXPCShellUtils.jsm");
 XPCOMUtils.defineLazyModuleGetter(this, "FileUtils",
                                   "resource://gre/modules/FileUtils.jsm");
 XPCOMUtils.defineLazyModuleGetter(this, "HttpServer",
                                   "resource://testing-common/httpd.js");
 XPCOMUtils.defineLazyModuleGetter(this, "NetUtil",
                                   "resource://gre/modules/NetUtil.jsm");