new file mode 100644
--- /dev/null
+++ b/dom/webidl/MediaCacheStatus.webidl
@@ -0,0 +1,19 @@
+/* -*- 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/.
+ *
+ * The origin of this IDL file is
+ * http://dvcs.w3.org/hg/html-media/raw-file/default/media-source/media-source.html
+ *
+ * Copyright © 2012 W3C® (MIT, ERCIM, Keio), All Rights Reserved. W3C
+ * liability, trademark and document use rules apply.
+ */
+
+[Func="mozilla::dom::MediaCacheStatus::Enabled"]
+interface MediaCacheStatus {
+  readonly attribute unsigned long blockSize;
+  readonly attribute unsigned long totalBlocks;
+  readonly attribute unsigned long occupiedBlocks;
+};
+

--- a/dom/webidl/moz.build
+++ b/dom/webidl/moz.build
@@ -660,16 +660,17 @@ WEBIDL_FILES = [
     'KeyIdsInitData.webidl',
     'LegacyQueryInterface.webidl',
     'LinkStyle.webidl',
     'ListBoxObject.webidl',
     'LocalMediaStream.webidl',
     'Location.webidl',
     'MatchGlob.webidl',
     'MatchPattern.webidl',
+    'MediaCacheStatus.webidl',
     'MediaDeviceInfo.webidl',
     'MediaDevices.webidl',
     'MediaElementAudioSourceNode.webidl',
     'MediaEncryptedEvent.webidl',
     'MediaError.webidl',
     'MediaKeyError.webidl',
     'MediaKeyMessageEvent.webidl',
     'MediaKeys.webidl',