How does this look to everyone?

page.diff

diff --git a/index.html b/index.html
index d23efde..9bba611 100755
--- a/index.html
+++ b/index.html
@@ -36,5 +36,12 @@ file, You can obtain one at http://mozilla.org/MPL/2.0/. -->
     <script src="js/vendor/jquery/dist/jquery.min.js" charset="utf-8"></script>
 
     <script src="js/main.js"></script>
+    <script>
+      window.addEventListener("message", function (event) {
+        if (event.data === 'whimsy:enabled') {
+          console.log("Whimsy!", event.data);
+        }
+      }, false);
+    </script>
   </body>
 </html>

whimsy.diff

diff --git a/lib/main.js b/lib/main.js
index 37df5e1..133734f 100644
--- a/lib/main.js
+++ b/lib/main.js
@@ -12,6 +12,7 @@
 
 'use strict';
 
+var pageMod = require('sdk/page-mod');
 var prefs = require('sdk/simple-prefs');
 var { Cu } = require('chrome');
 Cu.import('resource://gre/modules/UITelemetry.jsm');
@@ -104,6 +105,11 @@ exports.main = function () {
     });
   }
 
+  pageMod.PageMod({
+    include: '*',
+    contentScript: 'window.postMessage("whimsy:enabled", "*")'
+  });
+
 };
 
 exports.onUnload = function () {

Ship it!