diff -r 000000000000 -r 6474c204b198 browser/modules/Feeds.jsm
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/browser/modules/Feeds.jsm	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,52 @@
+/* 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/. */
+
+"use strict";
+
+this.EXPORTED_SYMBOLS = [ "Feeds" ];
+
+Components.utils.import("resource://gre/modules/XPCOMUtils.jsm");
+
+XPCOMUtils.defineLazyModuleGetter(this, "BrowserUtils",
+                                  "resource://gre/modules/BrowserUtils.jsm");
+
+const Ci = Components.interfaces;
+
+this.Feeds = {
+
+  /**
+   * isValidFeed: checks whether the given data represents a valid feed.
+   *
+   * @param  aLink
+   *         An object representing a feed with title, href and type.
+   * @param  aPrincipal
+   *         The principal of the document, used for security check.
+   * @param  aIsFeed
+   *         Whether this is already a known feed or not, if true only a security
+   *         check will be performed.
+   */
+  isValidFeed: function(aLink, aPrincipal, aIsFeed) {
+    if (!aLink || !aPrincipal)
+      return false;
+
+    var type = aLink.type.toLowerCase().replace(/^\s+|\s*(?:;.*)?$/g, "");
+    if (!aIsFeed) {
+      aIsFeed = (type == "application/rss+xml" ||
+                 type == "application/atom+xml");
+    }
+
+    if (aIsFeed) {
+      try {
+        BrowserUtils.urlSecurityCheck(aLink.href, aPrincipal,
+                                      Ci.nsIScriptSecurityManager.DISALLOW_INHERIT_PRINCIPAL);
+        return type || "application/rss+xml";
+      }
+      catch(ex) {
+      }
+    }
+
+    return null;
+  },
+
+};