So I've been using FF3.1b1 and have loved it. The speed improvements and cool new alt+tab style tab switcher have really been incredible. GMail has never loaded so quickly for me. The only thing I couldn't get working right away was Flash. So I dug around a bit and realized it was a matter of copying a file into the plugins folder of my beta installation.

Firefox has just released it's newest beta. In this beta is their new javascript engine called TraceMonkey which is, however, disabled by default. It's easy to enable though by toggling a simple option in about:config. Look for "javascript.options.jit.content" and set it to true.