Read more about this from Andreas Gal, Brendan Eich, Mike Shaver and Mike Schreopfer.

I am thrilled, with the initial optimizations delivering 10x-20x and even more performance than the JS engine in Firefox 3.0. The code is merged into the tree, and should appear with Firefox 3.1.

Now, if only that other browser would get a little better. On the brighter side, this might be just what Firefox needs to gain more share. Go!