Firefox asks for user name and password on internal sites
This article describes why Firefox may ask for a user name and password on internal/intranet sites (for example, a Sharepoint site) while Internet Explorer doesn't.
Many internal sites use NTLM authentication, which reuses your network login as a login for the site. In many organizations, Internet Explorer is configured to allow NTLM on the internal sites, but Firefox is not. You can configure Firefox on Windows to allow certain sites:
In the Location bar, type about:config, and press Enter.
The about:config "This might void your warranty!" warning page may appear. Click I'll be careful, I promise!, to continue to the about:config page.
In the about:config page, search for the preference network.automatic-ntlm-auth.trusted-uris, and double-click on it.
In the prompt that comes up, type a list of server you want to allow, separated by a comma and a space. For example, if you wanted to allow http://myinternalserver and http://anotherinternalserver, you would type in myinternalserver, anotherinternalserver.
Now that Firefox is configured to use NTLM on these sites, you should no longer be prompted for your user name and password.