Xvfb + Firefox
Resig has a bunch of unit tests he does to make sure jQuery works properly on whatever browser. Manually running and checking unit test results is annoying and time consuming. Let’s automate this. Update (May 2010): See this post for more details on automating xserver startup without having to worry about display numbers (:1, :2, etc). Combine something simple like Firefox and Xvfb (X Virtual Frame Buffer), and you’ve got a simple way to run Firefox without a visible display.