Thought I should write this down as it is fairly hard to find out there on the internet. When testing pages on XPPro using localhost Firefox can keep asking for a username and password even though permissions have been set. To get rid of this do the following

Frustrating isn’t it. Bet you thought it was you do something wrong but Firefox does have the ability to view your user account also. Ok do the following.
1) Open up Firefox and type in about:config as the url

2) In the Filter Type in ntlm

3) Double click the line that says “network.automatic-ntlm-auth.trusted-uris”

4) Type in localhost and hit enter

Hooray Firefox now can browse localhost. Enjoy