Firefox 5 and latest IE browsers cache redirects, therefore, if you hit http://www.domain.com and get redirect to http://www.domain.com/login.html
Then everytime you try and go to http://www.domain.com you will be redirected automatically to the login.html regardless as the browser makes the decision the redirect still stands without rechecking with the server.
i.e. it caches the redirect for speed.
You need to modify the script to include no cache headers before the redirect. I detailed this in your comments at:
Just in case others needed the info, and or the developer is not checking their comments. N