diff -r 000000000000 -r 6474c204b198 browser/components/shell/src/nsSetDefaultBrowser.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/browser/components/shell/src/nsSetDefaultBrowser.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,31 @@
+/* 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/. */
+
+/* 
+ * -setDefaultBrowser commandline handler
+ * Makes the current executable the "default browser".
+ */
+
+const Cc = Components.classes;
+const Ci = Components.interfaces;
+Components.utils.import("resource://gre/modules/XPCOMUtils.jsm");
+
+function nsSetDefaultBrowser() {}
+
+nsSetDefaultBrowser.prototype = {
+  handle: function nsSetDefault_handle(aCmdline) {
+    if (aCmdline.handleFlag("setDefaultBrowser", false)) {
+      var shell = Cc["@mozilla.org/browser/shell-service;1"].
+                  getService(Ci.nsIShellService);
+      shell.setDefaultBrowser(true, true);
+    }
+  },
+
+  helpInfo: "  -setDefaultBrowser Set this app as the default browser.\n",
+
+  classID: Components.ID("{F57899D0-4E2C-4ac6-9E29-50C736103B0C}"),
+  QueryInterface: XPCOMUtils.generateQI([Ci.nsICommandLineHandler]),
+};
+
+this.NSGetFactory = XPCOMUtils.generateNSGetFactory([nsSetDefaultBrowser]);