Probably an extension is causing this? Try to see if it happens in safe mode, please.

Well know I just feel silly, it turned out to be the extension tab control, I had to downgrade it to work with 3.6 again (it had updated when playing around with FF 5) and it seems version 0.5.2 was causing the issue, updating to 0.5.3 (last version compatible with FF 3.6) fixed it, thank!

Please click the Solved It button next to the answer that solved your Firefox support issue (it appears when you are logged in) so this thread gets marked as Solved to help other users who may have this same problem.