You might want to consider searching for an answer on the Apple/iTunes site instead of the FF site.

https://discussions.apple.com/community/itunes/itunes_for_windows

I did search the iTunes site, in a labyrinthian exercise. What I finally found was that iTunes says that there can "rarely" be problems loading to an iTunes account with Firefox and that one must be sure to have the latest version of Firefox( which I have). What I think I will do is simply uninstall my mp3 info with Amazon and start all over again. What should be simple isn't always so. I have also emailed Amazon to see what they say, if anything.