Am I right in thinking that your browser is completely crashing, or is it just getting slowed down? Does the problem go away when you go to pages without those ads? Does it ever happen on pages without those ads?
For me, the last two nights Firefox hasn't crashed (or at least it wasn't when I was actually 'on' MN, although MN might have been open when it crashed ifyswim), just run extremely slowly - one letter popping up then a wait for the next and having to wait ages for the text box to catch up with where I know I'd made a mistake.
I don't know what adds were on as I have now got used to completely ignoring them (sorry )