diff -r 000000000000 -r 6474c204b198 addon-sdk/source/lib/sdk/net/xhr.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/addon-sdk/source/lib/sdk/net/xhr.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,36 @@
+/* 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";
+
+module.metadata = {
+  "stability": "stable"
+};
+
+const { deprecateFunction } = require("../util/deprecate");
+const { Cc, Ci } = require("chrome");
+const XMLHttpRequest = require("../addon/window").window.XMLHttpRequest;
+
+Object.defineProperties(XMLHttpRequest.prototype, {
+  mozBackgroundRequest: {
+    value: true,
+  },
+  forceAllowThirdPartyCookie: {
+    configurable: true,
+    value: deprecateFunction(function() {
+      forceAllowThirdPartyCookie(this);
+
+    }, "`xhr.forceAllowThirdPartyCookie()` is deprecated, please use" +
+       "`require('sdk/net/xhr').forceAllowThirdPartyCookie(request)` instead")
+  }
+});
+exports.XMLHttpRequest = XMLHttpRequest;
+
+function forceAllowThirdPartyCookie(xhr) {
+  if (xhr.channel instanceof Ci.nsIHttpChannelInternal)
+    xhr.channel.forceAllowThirdPartyCookie = true;
+}
+exports.forceAllowThirdPartyCookie = forceAllowThirdPartyCookie;
+
+// No need to handle add-on unloads as addon/window is closed at unload
+// and it will take down all the associated requests.