Litmus is a tool for organized testing of Mozilla products. Litmus manages test cases and test results, and allows members of the general public to participate efficiently in the Mozilla testing process.
The types of tests Litmus organizes are tests that must be run manually - actually using specific products in a manner designed to flush out any bugs that may be hiding.
In testing with Litmus, you will need to first have an account registered and be logged in.
Once you are logged in, you will click run tests, enter details of the product you are testing, and be presented with groups of tests. Select a group from which you wish to perform testing, and you'll then be presented with individual tests. Any testing you are able to do helps improve the quality of Mozilla software. As you complete each test, you are invited to enter the results in the form of pass, unclear, or fail within the litmus interface:
It's important to note that any testing you are able to do in Litmus is helpful - the more people that participate, the more chance we have of stopping bugs before they make it into releases.
See also: http://wiki.mozilla.org/Litmus