diff -r 000000000000 -r 6474c204b198 xpcom/ds/nsIHashable.idl
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/xpcom/ds/nsIHashable.idl	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,24 @@
+/* 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 "nsISupports.idl"
+
+/**
+ * Represents an object that can be stored in a hashtable.
+ */
+[scriptable, uuid(17e595fa-b57a-4933-bd0f-b1812e8ab188)]
+interface nsIHashable : nsISupports
+{
+  /**
+   * Is this object the equivalent of the other object?
+   */
+  boolean equals(in nsIHashable aOther);
+
+  /**
+   * A generated hashcode for this object. Objects that are equivalent
+   * must have the same hash code. Getting this property should never
+   * throw an exception!
+   */
+  readonly attribute unsigned long hashCode;
+};