With Browsershot it takes a click to test your web design in different browsers

Browsershots is a web application that offers the fastest way to check your web design in different browsers – it does so in less than 10 minutes and eliminates the need to jump from one operating system to the other. This web application takes thumbnails of webpages on the Linux, BSD, Windows and Mac platforms and deploys over 50 different browser including Firefox, Internet Explorer, Konqueror, Opera, Navigator, Safari – and many other unknown browsers.

To check your web design, just enter the URL, check the browsers you’re interested in, customize — the screen resolutions and color depth — enable or not Javascript, Flash and Java, and hit submit. The more options/combinations you select the more time it takes to generate your request or screenshots. You can then click on the thumbnails and see for yourself how that operating system + browser renders your site

Browsershots supports Firefox 3 on both Linux and Windows.