<html>
<body>
<script type="text/javascript" charset="utf-8">
  // Only prevent unload on the first window close
  var unloadPrevented = false;
  window.onbeforeunload = function() {
    if (!unloadPrevented) {
      unloadPrevented = true;
      return false;
    }
  }
</script>
</body>
</html>