Mozilla has released the sixth beta for Firefox 4.0 on September 14th. This is a Fire Drill (unplanned) release and is being made available for testing purposes only.
New stuff in this release:
- Stability issue on Windows
- Rendering and keyboard/mouse focus issues on OSX related to plugins
For more info see the release notes for Firefox 4 Beta 6. All other items planned for the Beta 6 release have been rolled over to the upcoming Beta 7 release due in the later half of September.