When browsing, Firefox 4.0 will, every time and after a seemingly random interval of time since last launch (altough never higher than 5 minutes) start using 100% of one core, and just hang there. Waiting does not resolve the problem, I have to force quit the app. It is not linked to a particular website: it can happen anytime, anywhere (I'm using Chrome right now). I tried repairing permissions, nothing changed. I tried re-downloading Firefox, but nothing changed. I also disabled all extensions, which again did not solve the problem. The weirdest is that it happened all of a sudden, after I played with some Google Chrome files (I had disabled the autoupdate agent by creating empty files and setting chmod to 000, which worked). Deleting them and letting Chrome populate the drive with normal ones did not solve the problem. Any ideas/suggestions to try before I reinstall OS X? Thanks in advance.