diff -r 000000000000 -r 6474c204b198 toolkit/devtools/DevToolsExtensions.jsm
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/toolkit/devtools/DevToolsExtensions.jsm	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,46 @@
+/* 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 = ["gDevToolsExtensions"];
+
+Components.utils.import("resource://gre/modules/Services.jsm");
+
+let globalsCache = {};
+
+this.gDevToolsExtensions = {
+  addContentGlobal: function(options) {
+    if (!options || !options.global || !options['inner-window-id']) {
+      throw Error('Invalid arguments');
+    }
+    let cache = getGlobalCache(options['inner-window-id']);
+    cache.push(options.global);
+    return undefined;
+  },
+  getContentGlobals: function(options) {
+    if (!options || !options['inner-window-id']) {
+      throw Error('Invalid arguments');
+    }
+    return Array.slice(globalsCache[options['inner-window-id']] || []);
+  },
+  removeContentGlobal: function(options) {
+    if (!options || !options.global || !options['inner-window-id']) {
+      throw Error('Invalid arguments');
+    }
+    let cache = getGlobalCache(options['inner-window-id']);
+    let index = cache.indexOf(options.global);
+    cache.splice(index, 1);
+    return undefined;
+  }
+};
+
+function getGlobalCache(aInnerWindowID) {
+  return globalsCache[aInnerWindowID] = globalsCache[aInnerWindowID] || [];
+}
+
+// when the window is destroyed, eliminate the associated globals cache
+Services.obs.addObserver(function observer(subject, topic, data) {
+  let id = subject.QueryInterface(Components.interfaces.nsISupportsPRUint64).data;
+  delete globalsCache[id];
+}, 'inner-window-destroyed', false);