Well, there was a virus which firefox had to do with... showed up in c/documents and settings/applicaton data/Mozilla Firefox/ or something along those lines. Like I said, it may have been a fasle posative...
it's not a virus in mozilla, it's probably some kind of java worm of something like that, which uses the java application in the browser to enter the computer.
Like u have a virus which is in C:\windows\system32, it doesn't mean that ur windows came with a virus, some virus just got into ur computer and went to that folder.
Or something else, but I highly doubt that the virus came with firefox.