spearhead - 2008-03-17

Dear all,
I have joined an RHEL server with our windows AD for single sign on pages. After hosting the pages users can  browse the pages easily with IE and can get their username in php page. But the problem is when users try to use firefox for browsing those pages. It gives the below error messgae:

Authorization Required
This server could not verify that you are authorized to access the document requested.Either you supplied the wrong credentials(e.g., bad password) or your browser doesn't understand how to supply the credentials requested.
Also tried this below:
Firefox: about:config → network.negotiate-auth.trusted-uris

but no luck. Any help please.