Chrome or Firefox will not accept credentials when logging in using ADFS server

You may find that Google Chrome or FireFox 3.5+ keeps prompting for authentication when you are redirected to your ADFS 2.0 server.  This is also known to affect Fiddler.  See "AD FS 2.0: Continuously Prompted for Credentials While Using Fiddler Web Debugger" on TechNet.

This happens when Windows Authentication Extended Protection is enabled in IIS on either the ADFS proxy, ADFS back-end server, or both.

Here's how to turn Extended Protection off:

• Login to the ADFS proxy server and open the Internet Information Services (IIS) Management console.
• Navigate to the adfs\ls virtual directory under the Default Web Site.

• Double-click Authentication to open the authentication methods for the ADFS\LS directory.
• Select Windows Authentication and then click Advanced Settings in the Actions pane.
• Set Extended Protection to Off.

• Make sure you do this for all your ADFS proxy and ADFS back-end servers.