Comment 15 for bug 1638610

(In reply to Boris Zbarsky [:bz] from comment #8)
> Or we could have a "in unload prompt" flag that gets propagated to timeouts
> set while that flag is set and any code those timeouts run etc.

var gotbeforeunload = false;
setInterval(function() {
 if (gotbeforeunload) {
   location.href = "foo";
 }
}, 100);
onbeforeunload = function() { gotbeforeunload = true; };

would defeat that, AIUI. :-(

(and I've seen patterns like this in use on trappy sites before :-( )

Really, the whole beforeunload thing needs to go away, but then there's the rest of the web to think of. :-(