What you could try, just to eliminate possible causes, is to setup SSH (Putty) as a proxy to all webUI's within the Kerberized cluster, connect Putty, setup Firefox to use the proxy, kinit locally (Windows) and try again.
I can't help you much with the Windows Kerberos client cause I am on Mac. Check for ways to verify if the kinit was really successful.
You could also use curl on Windows ( curl --negotiate
-u: "http://address:port") to do the ticket forwarding in stead of the browser.