Windows Auto Sign in works only with Microsoft Windows. Follow below steps and make changes to your browser settings to enable "One Click Sign In" using Integrated Windows Authentication.
Select the security Tab and then Trusted zone then custom settings. Scroll to the bottom and make sure that the User Authentication Logon is set to “Automatic Logon with current username and password”.
NTLM can be enabled in Firefox by editing the "about:config". You can automatically set the value (VB script) or manually change the settings as given below.
Please download this script and run it. Make sure to close Firefox browser before you run this script.
This will show all the settings for Firefox. In this list find this key “network.automatic-ntlm-auth.trusted-uris.” This is a comma-delimited list of all host names that you want to use NTLM with. Right click this entry and select "Modify". Enter "cable.comcast.com and click "OK". Restart the FF browser and NTLM should be working from now.