“Basically firefox logs all kinda of URL data in it’s history.dat file, this little script will set a really large topic and Firefox will then save that topic into it’s history.dat.. The next time that firefox is opened, it will instantly crash due to a buffer overflow — this will happen everytime until you manually delete the history.dat file — which most users won’t figure out.
this proof of concept will only prevent someone from reopening their browser after being exploited. DoS if you will. however, code execution is possible with some modifcations.”
packet storm via Juha