Here's a tip for Firefox. An extension called BugMeNot enables you to right click on "general" forms and say "Login with BugMeNot." Firefox will call the BugMeNot extension which looks up in an external database login information. For instance, www.nytimes.com requires a login, which is a great place to test it out.
http://extensionroom.mozdev.org/more-info/bugmenot