load-into-the-iframe.html

Enable keyboard shortcuts

<!DOCTYPE html>

<html>

  <head>

    <meta charset="utf-8">

  </head>

  <body>

    <iframe sandbox="allow-scripts"></iframe>

    <script>

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

      let sandbox = new URL(location.href).searchParams.get("sandbox");

      if (sandbox) {

        frame.sandbox = sandbox;

      // We're the popup (i.e. a top frame).  Load into the iframe the page

      // trying to modifying the top frame and transmit the result to our

      // opener.

      onmessage = function(e) {

        opener.postMessage(e.data, "*")

      frame.src = "iframe-that-performs-top-navigation-on-popup.html";

    </script>

  </body>

</html>