Testing intranet site under different accounts

We have ASP.NET intranet site that uses Windows authentication. Developers have a set of test Windows accounts (local, not domai开发者_Go百科n) with different roles on their boxes. All browsers that we use (IE, Chrome, FF) automatically logon with currently logged in user. How do we setup the browsers to ask for credentials when the site is opened? I tried setting "Prompt for user name and password" in security parameters of intranet zone in IE but that didn't help. But the site needs to be tested in all browsers mentioned above. So how do you test your sites in similar environment?

p.s. Including/excluding the current user to/from required Windows groups is not an option as it requires re-logon.

This is a shot in the dark (I don't even have Windows handy at the moment and can't check), but did you try running browsers via runas (command-line utility, or similar setting in the program shortcut properties)? If it does the trick, you can create shortcuts to launch browsers with different credentials.