No problems here with FF.
Assuming that you have not made any other changes whatever, I Suggest you clear your cookies, IE cache and run ipconfig /flushdns from a command prompt (Run, CMD).
If you have made changes (e.g. new applications, new hardware, MS updates etc.) then all bets are off, and try going back to a System restore point from before the problem occurred.
Also make sure that your AV is up-to-date and active (ditto malware).
SD