Disclaimer: I am an avid user of FireFox.
I am kinda tired of updating FireFox twice a week. It is a great product but the arrogant idiots who claimed FireFox is secure are just that: idiots. Did you really think that Microsoft was the only software company in the world writing vulnerable applications? At least with IE, I don't get bugged every other day to fix a critical flaw.
Alas, I digress. Here is the link detailing the vulnerability:
here.