Firefox 3.0.1, the latest version. Mozilla is the maker of Firefox, and the 5.0 in another post actually refers to the software suite of which Firefox is a part. And I still use Windows 2000 Professional, which is starting to cause issues 'cause they don't put out new software for it. For instance, there's a new web browser plugin called "Silverlight" that a lot of web sites are starting to use, but I can't install, because there isn't a version out there for Firefox/Windows 2000, only XP or Vista. Plus I can't install IE 7.0, let alone the new 8.0 they're about to put out. You may want to have people post their computer's OS version also, because the same browser may perform differently on a different OS.