diff -r 000000000000 -r 6474c204b198 browser/metro/components/DirectoryProvider.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/browser/metro/components/DirectoryProvider.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,44 @@
+/* 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/. */
+
+const Cc = Components.classes;
+const Ci = Components.interfaces;
+
+Components.utils.import("resource://gre/modules/XPCOMUtils.jsm");
+
+// -----------------------------------------------------------------------
+// Directory Provider for special browser folders and files
+// -----------------------------------------------------------------------
+
+const NS_APP_CACHE_PARENT_DIR = "cachePDir";
+
+function DirectoryProvider() {}
+
+DirectoryProvider.prototype = {
+  classID: Components.ID("{ef0f7a87-c1ee-45a8-8d67-26f586e46a4b}"),
+  
+  QueryInterface: XPCOMUtils.generateQI([Ci.nsIDirectoryServiceProvider]),
+
+  getFile: function(prop, persistent) {
+    if (prop == NS_APP_CACHE_PARENT_DIR) {
+      let dirsvc = Cc["@mozilla.org/file/directory_service;1"].getService(Ci.nsIProperties);
+      let profile = dirsvc.get("ProfD", Ci.nsIFile);
+
+      let sysInfo = Cc["@mozilla.org/system-info;1"].getService(Ci.nsIPropertyBag2);
+      let device = sysInfo.get("device");
+      switch (device) {
+        default:
+          return profile;
+      }
+    }
+
+    // We are retuning null to show failure instead for throwing an error. The
+    // interface is called quite a bit and throwing an error is noisy. Returning
+    // null works with the way the interface is called [see bug 529077]
+    return null;
+  }
+};
+
+this.NSGetFactory = XPCOMUtils.generateNSGetFactory([DirectoryProvider]);
+