Hi, If it's Basic auth, please check if this happens in a [https://support.mozilla.org/en-US/kb/Managing-profiles new profile]. If it's okay, you can later [https://support.mozilla.org/en-US/kb/Recovering%20important%20data%20from%20an%20old%20profile?s=profile&r=1&e=sph&as=s copy the needed personal data] from the old profile. Firefox stores your personal data and settings in another location separate from its [http://kb.mozillazine.org/Installation_directory files/folder]. A new profile would have the default Firefox settings ('''Tools''' ('''Alt''' + '''T''') > [https://support.mozilla.org/en-US/kb/Options%20window '''Options'''], and [http://kb.mozillazine.org/About:config about:config] ), and usually would also be empty of any '''Extensions''' and themes ('''Appearance''') in Tools > Add-ons) and their settings. Also, a new profile would have no previous stored website data/settings etc., ('''Tools''' > [https://support.mozilla.org/en-US/kb/Clear%20Recent%20History '''Clear Recent History''']). [https://support.mozilla.org/en-US/kb/Profiles?s=profile&r=2&e=sph&as=s Profiles Howto] [http://kb.mozillazine.org/Profile_folder_-_Firefox Profile Folder & Files] [http://kb.mozillazine.org/About:config_entries about:config Entries] For NTLM authentication, you can try to automatically trust the domain in the [http://kb.mozillazine.org/Network.automatic-ntlm-auth.trusted-uris network.automatic-ntlm-auth.trusted-uris] list in [http://kb.mozillazine.org/About:config about:config], eg. domain.com Not sure, but for Kerberos, I think you would have to use '''network.negotiate-auth.trusted-uris''' instead.

Thank you for this - I have tried all you have said and whilst it has not made matters any worse, it has not resolved my problem. It has been usefull for me in finding out more behind the scenes stuff for Firefox which I am sure will come in handy in the future. However it does not solve my current problem so are there any other suggestions/ answers please? Phil

It would be also be helpful to contact the IT/Network support for the authentication mechanism in use. If it's NTLM, you can also try the variations like .site.com or the full name/exact name. You can also try to temporarily test without using a proxy: '''Tools''' ('''Alt''' + '''T''') > '''Options''' > '''Advanced''' > '''Advanced''' > '''Network''' > '''Settings''' > '''No proxy'''. [https://support.mozilla.org/en-US/kb/Options%20window%20-%20Advanced%20panel?as=u Options > Advanced]