Firefox and Chrome are known to be slow on localhost when IP6 is enabled. In previous versions of Windows, the simplest fix is to comment out this line from the hosts file,
I'd do what Tim Schneider mentioned. Also mentioned by this James here:
http://theycallmemrjames.blogspot.com/2010/09/firefox-is-really-slow-testing-sites-on.html
"Double-click on ipv4OnlyDomains, and type localhost "