The latest version of keyscrambler personal (free version) doesn't play well with beef TACO, preventing login to basic sites, e.g. gmail. This user opted to uninstall TACO and reinstall keyscrambler, test machine runs WinXP SP3 and Firefox 4.0.1
relevant linkskeyscrambler
http://www.qfxsoftware.com/keyscrambler
http://support.mozilla.com/en-US/questions/787241beef TACO
https://addons.mozilla.org/en-us/firefox/addon/beef-taco-targeted-advertising/