I am running the latest version of Firefox, v3.0.6. And I already mentioned in my first port that I tried uninstalling and reinstalling it. Even staring it in Safe mode does not help.
As for the changes I made to the system, well I recently formatted one of my partitions and also removed some fonts that I don't use. But the partition that I formatted was not the one on which I had installed Firefox on and I don't see how removing fonts could be a problem, as Opera seems to be working fine as with every other application.