The Tor Browser / file revision

 <script>

 // HACK: This is not an ideal way to deliver chrome messages

 // to a innef frame content but seems only way that would

 // make `event.source` an this (outer frame) window.

 window.onmessage = function(event) {

   var frame = document.querySelector("iframe");

   var content = frame.contentWindow;

   // If message is posted from chrome it has no `event.source`.

   if (event.source === null)

     content.postMessage(event.data, "*");

 };

 // Hack: Ideally we would have used srcdoc on iframe, but in

 // that case origin of document is either content which is unable

 // to load add-on resources or a chrome to which add-on resource

 // can not send messages back.

 document.documentElement.style.overflow = "hidden";

 document.documentElement.innerHTML = atob(location.hash.substr(1));

 </script>