Of course i understand that as a webmaster you need to check your site for cross browser compatibility issues, but then again why install all of these different browsers when you can get multi browser screenshots from online sites like http://browsershots.org and http://www.browsercam.com?
My primary browser is FireFox, however, I have IE, Opera, and Chrome to test my websites and provide support for my customers who decide to use other browsers.
FireFox 3 (Most of the time) IE 7 (because some sites do not load properly on FF) Opera (because some sites do not load properly on both FF and IE - rare incident) Google Chrome (because I'm interested to give it a try)