Looking at the virus scan in your screen shot, what is the file khfcwmm.dll doing in your windows directory? Looks suspicious to me. I'd make sure you get "14 threats found" cleaned up first.
Then download the tool to completely uninstall norton:
http://service1.symantec.com/Support...05033108162039
If it still doesn't work try restarting firefox with a new profile:
firefox -p
If it still doesn't work, try reinstalling firefox. Your settings should be retained, if they aren't trashed already.