Start Firefox in Use Troubleshoot Mode in Firefox to check if one of the add-ons is causing the problem (switch to the DEFAULT theme: Tools > Add-ons > Themes).

• Don't make any changes on the Safe mode start window.

See:

• Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems

It works fine in safe mode, but do you have any idea of which add on or extension may be causing this because the only reason i really use firefox is because of the extensions and add ons so if I can't use them it's pointless!!!

Also firefox 4 rc still memory leaks like hell on my computer