Update: I got a lot of comments on my post. I am trying to answer them as they come in, so check back after you leave a comment.

Brendan Eich and Mike Shaver have posted an update on our progress on TraceMonkey. There has been a lot of buzz around Google’s new Chrome browsers and its V8 JavaScript VM. Some voices have claimed that V8 is several times faster than TraceMonkey. We did some head to head comparisons and these claims don’t match our observations.

We used Apple’s SunSpider benchmarks for our tests. Depending on the OS and machine configuration we are 1.18x to 1.28x faster than V8. Since V8 is only available for Windows, we didn’t perform any tests on MacOSX and Linux, both of which we support already. Our latest builds also work on ARM, by the way.

I am sure you can derive different results by tweaking the benchmarks or designing entirely new custom benchmarks alltogether, but since SunSpider has been used fairly intensively in the past two years to measure the evolution of JavaScript performance in Safari, Firefox, Opera, and IE, I think SunSpider is probably the most reliable cross-platform benchmarking tool at this point (which doesn’t say that its a particularly good one, its just the best we have right now.)

Talking about IE, our tests also indicate that we are about 15 times faster than IE 7, and about 5 times faster than IE 8 beta on the SunSpider aggregate scores.

If you want to give TraceMonkey a try, take a look at our nightly builds. You can enable the JIT in the about:config settings. The nightly builds are certainly not ready yet for wide-spread use, but we have improved stability significantly since our initial preview release. Firefox with TraceMonkey enabled is now my default browser, and I am writing this post with it.