diff -r 000000000000 -r 6474c204b198 dom/interfaces/events/nsIDOMBeforeUnloadEvent.idl
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/dom/interfaces/events/nsIDOMBeforeUnloadEvent.idl	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,26 @@
+/* -*- Mode: IDL; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* 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 "nsIDOMEvent.idl"
+
+/**
+ * The nsIDOMBeforeUnloadEvent interface is the interface for events
+ * sent to handlers of the "beforeunload" event. This event is
+ * non-standard. Interface derived from Microsoft IE's event
+ * implementation.
+ *
+ * http://msdn.microsoft.com/library/default.asp?url=/workshop/author/dhtml/reference/events.asp
+ *
+ */
+
+[scriptable, builtinclass, uuid(ee7b8943-440e-4cc3-b25e-c17c8a821d8b)]
+interface nsIDOMBeforeUnloadEvent : nsIDOMEvent
+{
+  /**
+   * Attribute used to pass back a return value from a beforeunload
+   * handler
+   */
+           attribute DOMString          returnValue;
+};