Mozilla has completed the merge for Thunderbird 9 on the Beta release channel on November 16, 2011. The latest version of Thunderbird Beta has the following changes:

• Added an opt-in system for users to send performance data back to Mozilla to improve future versions of Thunderbird
• 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
• and numerous other platform fixes

Please see the complete list of changes in this version.

You can get Thunderbird 9 Beta (as well as Thunderbird 10 Earlybird) here. Lightning users: you will need up update to version 1.1 of Lightning for Thunderbird 9 Beta or version 1.2a2 for Thunderbird 10 Earlybird.