Firefox browser contains network settings under Tools-->Options-->Advanced-->Network-->Settings and there is an option to do auto detect proxy settings, how should I enable this? Currently this is manually configured and its possible for users to bypass and use the internet directly. We use a variety of browsers (firefox, IE, chrome, safari, opera) on win xp, win 2003, win vista machines. How should I enable this so that the end user cannot manipulate the settings on his browser to by pass security.

I have configured a squid cache proxy server for this purpose.