Firefox 4 beta 7 is out, and as you read, it really looks much better, fast and nearly complete. Mozilla enabled graphics acceleration on both Windows and Mac OS X and integrated Sync and the previous feature Panorama.
Mozilla says that they worked hard to bring impressive engine for web pages, interpreting webapps and games. The chart below contains three benchmark tests, including their own, shows what looks like some serious improvements.
Mozilla also planes for some hardware-based graphics acceleration. Guys over there made a quick demonstration video for how JavaScript performance can speed along with the apps: