I benchedmarked the JavaScript engines of Internet Explorer 8, Firefox 3.5 and Chrome 2.0.172.33 using the SunSpider JavaScript Benchmark. Here are the results:

Internet Explorer 8: 6071.4ms (results)
Firefox 3.5: 1492.8ms (results)
Google Chrome 2.0.172.33: 749.8ms (results)

In conclusion, IE is still inexplicably shit, taking 6 seconds overall to complete the various tasks. Google Chrome still has the faster engine, despite the release of Firefox 3.5 yesterday. Whoop.