If you haven’t heard of Litmus before, you’re definitely missing out. Litmus is a browser testing service. It works like this – you login, enter a url, and then Litmus snaps screenshots of your site in multiple browsers across multiple operating systems.

Screenshot of Litmus browser test results

With Litmus, you can test in IE 5/6/7/8, Firefox, Safari, Chrome, Opera, and a few more browsers. Plus, most browsers have multiple versions available for testing.

You can really tell that the functionality and design of Litmus has been given a lot of thought. Some of the features I really like are:

1) Publishing screenshots – You can make screenshots public to show a client/colleague. Check out an example here.

2) Validation – Litmus will automatically validate your html and css code.

3) Notifications – You can be notified via GTalk, AIM, or Twitter when your screenshots have finished.

4) Compatibility tracking – You can mark browsers as compatible/not compatible for each screenshot so you know what’s left to fix.

Litmus also offers email client testing and it looks like they’ll soon be offering mobile device (iPhone, Blackberry, Android) testing as well!