User-Agent: Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.1; WOW64; Trident/4.0; SLCC2; .NET CLR 2.0.50727; InfoPath.3; .NET4.0C; .NET4.0E; .NET CLR 3.5.30729; .NET CLR 3.0.30729; MS-RTC LM 8) Build Identifier: Mozilla/5.0 (Windows; U; Windows NT 6.1; en-GB; rv:1.9.2.10) Gecko/20100914 Firefox/3.6.10 When trying to access a Single Sign On web application which authenticate against an Active Directory Federation Service. Firefox will continuously prompt for credentials on Window 7. Reproducible: Always Steps to Reproduce: 1. Go to a web application that uses ADFS 2.0 using Window 7 2. 3. Actual Results: Login prompts reappears continuously after correct credentials are supplied. Expected Results: Login successful after entering the correct credential once. We can work around the issue by setting network.auth.force-generic-ntlm to true OR Changing the registry HKLM\System\CurrentControlSet\Control\Lsa\LmCompatibilityLevel to 2 (Use NTLM). By default, LmCompatibilityLevel on Window 7 is set to 3 (Use NTLMv2 Only)