<html>
  <head>
    <meta charset="utf-8">
    <script>
      addEventListener("pageshow", function() {
        var bc = new BroadcastChannel("browser_browsingContext");
        function frameData() {
          var win = SpecialPowers.wrap(frames[0]);
          bc.postMessage(
            { framesLength: frames.length,
              browsingContextId: win.docShell.browsingContext.id,
              outerWindowId: win.docShell.outerWindowID
            });
        }

        bc.onmessage = function(event) {
          if (event.data == "createiframe") {
            let frame = document.createElement("iframe");
            frame.src = "dummy_page.html";
            document.body.appendChild(frame);
            frame.onload = frameData;
          } else if (event.data == "nextpage") {
            bc.close();
            location.href = "onload_message.html";
          } else if (event.data == "queryframes") {
            frameData();
          } else if (event.data == "close") {
            bc.postMessage("closed");
            bc.close();
            window.close();
          }
        }
        bc.postMessage("pageshow");
      });
    </script>
  </head>
  <body>
    This file posts a message containing "pageshow" to a BroadcastChannel and
    keep the channel open for commands.
  </body>
</html>