popup_override.js

if (window.___dialogEncountered === undefined) {
  window.___dialogEncountered = false;
}

if (window.___dialogReturnValue === undefined) {
  window.___dialogReturnValue = false;
}

window.___dialogHandler = function(dialogType) {
  window.parent.___dialogEncountered = dialogType;
  return window.parent.___dialogReturnValue;
};

window.alert = function() { return window.___dialogHandler('alert') };
window.confirm = function() { return window.___dialogHandler('confirm') };
window.prompt = function() { return window.___dialogHandler('prompt') };
window.onbeforeunload = function() {}; // returning anything from this function causes popup

// handle frames
for (var i=0; i < window.frames.length; i++) {
  try {
    window.frames[i].alert = function() { return window.parent.___dialogHandler('alert') };
    window.frames[i].confirm = function() { return window.parent.___dialogHandler('confirm') };
    window.frames[i].prompt = function() { return window.parent.___dialogHandler('prompt') };
    window.frames[i].onbeforeunload = function() {};
  } catch(e) {
    // frame src is most likely from a different domain
  }
}