This applies to Windows 7 and Firefox 3.52. I don’t know it works on other versions.

If your Firefox redirects localhost to www.localhost.com and makes you crazy follow the steps:

• Open C:\Windows\System32\drivers\etc\hosts and remove # from 127.0.0.1       localhost. Don’t forget to open file with administrator rights otherwise you cannot save it. If  you can’t find the way, copy the file to desktop, edit and move to the original location.
• Open network connection properties and disable IPv6