Thunderbird 9 has been released on December 20th, 2011. Current Thunderbird 8.0.0 users can update via Help > About Thunderbird. Lightning users, after you have updated to Thunderbird 9.0, your calendars will be broken. To fix this go Tools > Add-ons and then in your add-ons list, at the top of the list click the gear button and select Check for Updates. Lightning will update to version 1.1 (other add-ons may be updated at this time as well) and once you restart Thunderbird, your calendars will be working again.
What’s new in Thunderbird 9.0:
- Thunderbird is based on the new Mozilla Gecko 9 engine
- New opt-in system for users to send performance and usability data back to Mozilla to improve future versions of Thunderbird
- Additional support for Personas in the compose and address book windows
- Better keyboard handling for attachments
- Windows users can hide the menu bar (and show it with the “alt” key)
- Several user interface fixes and improvements
- Fixed several security issues
Users can also manually download Thunderbird 9.0 via getthunderbird.com and then install over your existing Thunderbird 8.0.x install. The next scheduled released is Thunderbird 10.0 on January 31st, 2012.