If you use FireFox to debug on Windows Vista, you most likely have noticed how ridiculously slow it is rendering localhost requests versus Internet Explorer. No, this isn’t a conspiracy, just an issue with IPv6, FireFox, and Windows Vista.
To fix this issue, do the following:
1) Open up about:config in your FireFox browser
2) Filter or scroll down to network.dns.disableIPv6 and set this value to true
3) Restart FireFox and you should be good to go!