I've tested<p><a href="http://nightly.mozilla.org/js-preview.html" rel="nofollow">http://nightly.mozilla.org/js-preview.html</a><p>with my simple benchmark loop (two floating point additions per pass) and it's really better:<p>300M passes of loop, time in seconds:<p>0.88 Firefox 4b6<p>2.26 Firefox 3.6.6<p>which is approximately 2.5 times faster.<p>Now that particular loop executes at the same speed as ActionScript 3 (in Flash 10) with explicit typing. That's the big achievement for Mozilla.
Can't get over how young the programmer team looks. Compared say, to Lars Bak who is 45-ish and working on V8... Whatever happened to the grizzled JIT writers?