From MozillaZine Knowledge Base
This preference determines which sites are allowed to automatically authenticate via NTLM. If the user requests a site that authenticates with NTLM that is not in this list, the user will be prompted for login details.
Possible values and their effects
A comma and space delimited list of URLs that are allowed to automatically authenticate via NTLM. (Default: empty string)
First checked in
Has an effect in