diff -r 000000000000 -r 6474c204b198 xpcom/ds/nsIPersistentProperties2.idl
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/xpcom/ds/nsIPersistentProperties2.idl	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,69 @@
+/* -*- Mode: C++; 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 "nsIProperties.idl"
+
+interface nsIInputStream;
+interface nsIOutputStream;
+interface nsISimpleEnumerator;
+
+[scriptable, uuid(283EE646-1AEF-11D4-98B3-00C04fA0CE9A)]
+interface nsIPropertyElement : nsISupports {
+  attribute AUTF8String key;
+  attribute AString value;
+};
+
+[scriptable, uuid(1A180F60-93B2-11d2-9B8B-00805F8A16D9)]
+interface nsIPersistentProperties : nsIProperties
+{
+  /**
+   * load a set of name/value pairs from the input stream
+   * names and values should be in UTF8
+   */
+  void load(in nsIInputStream input);
+
+  /**
+   * output the values to the stream - results will be in UTF8
+   */
+  void save(in nsIOutputStream output, in AUTF8String header);
+
+  /**
+   * call subclass() to make future calls to load() set the properties
+   * in this "superclass" instead
+   */
+  void subclass(in nsIPersistentProperties superclass);
+
+  /**
+   * get an enumeration of nsIPropertyElement objects,
+   * which are read-only (i.e. setting properties on the element will
+   * not make changes back into the source nsIPersistentProperties
+   */
+  nsISimpleEnumerator enumerate();
+
+  /**
+   * shortcut to nsIProperty's get() which retrieves a string value
+   * directly (and thus faster)
+   */
+  AString getStringProperty(in AUTF8String key);
+
+  /**
+   * shortcut to nsIProperty's set() which sets a string value
+   * directly (and thus faster). If the given property already exists,
+   * then the old value will be returned
+   */
+  AString setStringProperty(in AUTF8String key, in AString value);
+};
+
+
+%{C++
+
+#define NS_IPERSISTENTPROPERTIES_CID \
+{ 0x2245e573, 0x9464, 0x11d2, \
+  { 0x9b, 0x8b, 0x0, 0x80, 0x5f, 0x8a, 0x16, 0xd9 } }
+
+#define NS_PERSISTENTPROPERTIES_CONTRACTID "@mozilla.org/persistent-properties;1"
+
+%}
+