Firefox, good choice. That's what I use. (Though to be fair, Chrome, Opera, and Safari are also good browsers, and I've even heard Internet Explorer 9 is halfway decent (not that I'd ever use it).)
Now, have you made sure that your computer is virus-free? Some viruses can be tough to get rid of once they're on a system; I wouldn't trust that system before reinstalling everything (including the OS). If that seems like overkill, at least run several different, well-reputed virus scanners, since each individual antivirus software has gaps.
edited 19th Dec '11 9:54:20 PM by Enthryn