Mozilla released the second Release Candidate for Firefox 4.0 on March 18th. New in this release:
- Blacklisted a few invalid HTTPS certificates
- Updated localizations for 29 locales
- Added Vietnamese localization, bringing the total languages available in Firefox 4 to 83
For more info see the release notes for Firefox 4 RC2. The next planned release should be the official release of Firefox 4 which is scheduled for March 22nd, 2011.