I installed IIS on a reformatted computer and when trying to access the home page using Firefox I was asked for my username and password. After many tries and permission checkings (check this first!) I used IE and it worked€¦ I googled a little bit and found this solution:

1. Open up Firefox and type about:config in the url field

2. In the Filter Type in ntlm

3. Double click €œnetwork.automatic-ntlm-auth.trusted-uris€ and type in localhost and hit enter

After I did that everything worked ok.