diff -r 000000000000 -r 6474c204b198 modules/libpref/public/nsIPrefBranchInternal.idl
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/modules/libpref/public/nsIPrefBranchInternal.idl	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,17 @@
+/* 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/. */
+
+#include "nsIPrefBranch2.idl"
+
+/**
+ * An empty interface to provide backwards compatibility for existing code that
+ * bsmedberg didn't want to break all at once. Don't use me!
+ *
+ * @status NON-FROZEN interface WHICH WILL PROBABLY GO AWAY.
+ */
+
+[scriptable, uuid(355bd1e9-248a-438b-809d-e0db1b287882)]
+interface nsIPrefBranchInternal : nsIPrefBranch2
+{
+};