message: dont crash because firefox's alert is read only
diff: @@ -448,7 +448,11 @@ BrowserBot.prototype._modifyWindow = function(win) {
  // find it later. This is slightly different from uniqueId.
  win.seleniumKey = BrowserBot.uniqueKey++;
  + try {
  this.modifyWindowToRecordPopUpDialogs(win, this);
  + } catch (ex) {
  + console.error(ex);
  + }
  //Commenting out for issue 1854
  //win[this.uniqueId] = 1;
  