Mozilla has rolled out Firefox 4 beta 10 with some fixes, but the main emphasis is to add stability as compare to beta 9. The Firefox development team has plan to release last beta of Firefox 4 by the end of this month before release candidate.

Firefox 4 Beta 10 New Features:

Compatibility and stability improvements when using Adobe Flash on Mac OS X

Improvements in memory usage

Support for a graphics driver blacklist to improve stability