After the release of the final Firefox 4 beta 9 the new beta 10 pre (4.0b10pre) is available from the nightly downloads.

It looks like 10 or 11 will be the last beta, after that Mozilla will release from one to three release candidate (RC) versions. After RC versions follows the actual release of Firefox 4.0, which the Firefox public has been waiting for more than half a year. This gives add-on developers a little more time to update or upgrade their add-ons to work with FF4 branch as well.