Editor/tools/firefox-addon-sdk-1.16/lib/sdk/ui/frame/view.html

<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>