At present a web-site can make message on window.onbeforeunload too long and spoof it to confuse users. added to that, tricks like the one at http://www.internetisseriousbusiness.com/ can make user accidentally click "Cancel" instead of "OK" So Firefox should. 1. show site message in different color/background. 2. reduce built-in text in the confirm question and keep them together. ======================== current =========================== Are you sure you want to navigate away from this page? Press OK to continue, or Cancel to stay on the current page. [OK] [Cancel] ============================================================ =================== proposed ==================== Do you want to leave this page? [Leave] [Stay] ================================================= 3. show site name for which the pop-up message is shown. (shorten it to show only relevant part of name to avoid domain name spoof/hack) See attached onbeforeunload.png

I believe Bug 246365 is a dupe of this. I like the mockup you provided. With a little bit of tweaking, this could be a great improvement.