Neowin reader has compiled the results of the SunSpider javascript Benchmark test for each of the different browsers. All of the tests below were performed on the same Windows machine, and the Firefox 3 nightly builds definitely came out on top. Here are the results sorted from best to worst:

Firefox 3 Nightly (PGO Optimized): 7263.8ms

Firefox 3 Nightly (02/25/2008 build): 8219.4ms

Opera 9.5.9807 Beta: 10824.0ms

Firefox 3 Beta 3: 16080.6ms

Safari 3.0.4 Beta: 18012.6ms

Firefox 2.0.0.12: 29376.4ms

Internet Explorer 7: 72375.0ms

You can download the top performing build (#1 in Neowin post) here.