Import XULRunner and make it produce the generic stub

application/xulrunner/examples/simple/content/simple.js

@@ -0,0 +1,17 @@
+/* vim:set ts=2 sw=2 sts=2 et cin: */
+/* 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/. */
+
+function onButtonClick() {
+  var textbox = document.getElementById("textbox");
+
+  var contractid = (textbox.value % 2 == 0) ?
+      "@test.mozilla.org/simple-test;1?impl=js" :
+      "@test.mozilla.org/simple-test;1?impl=c++";
+
+  var test = Components.classes[contractid].
+      createInstance(Components.interfaces.nsISimpleTest);
+
+  textbox.value = test.add(textbox.value, 1);
+}

application/xulrunner/examples/simple/content/simple.xul

@@ -0,0 +1,20 @@
+<?xml version="1.0"?>
+# vim:set ts=8 sw=8 sts=8 noet:
+# 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/.
+
+<?xml-stylesheet href="chrome://global/skin/" type="text/css"?>
+
+<!DOCTYPE window SYSTEM "chrome://simple/locale/simple.dtd">
+
+<window
+  id    = "simple"
+  title = "&simple.title;"
+  xmlns = "http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul">
+  <script src="chrome://simple/content/simple.js"/>
+  <vbox>
+    <textbox id="textbox" value="&simple.textValue;" flex="1"/>
+    <button id="button" label="&simple.buttonLabel;" oncommand="onButtonClick();"/>
+  </vbox>
+</window>