Jack, I know this is an obvious solution, but have you tried clearing your FF cache? Also, it helps to delete TK's cookie.
What OS and version of FF are you running on? Do you have Mozilla 3.6?
Are you banned at home or the office? Could be a network or an ISP issue. Try resetting your router and modem.
If all else fails, reinstall FF. OR contact your ISP and tell them you're having problems.