Thunderbird Release Notes
v.12.0.1, released: April 30, 2012
FIXED - Fix various issues relating to new mail notifications and filtering on POP3 based accounts
FIXED - Fixes an occasional startup crash seen in TB 12.0
FIXED - Fixes an issue with corrrupted message bodies when using movemail
Unresolved - If you are unable to view content for your RSS feeds in the Wide View Layout, you may need to disable the Lightning Calendar add-on if you have it installed or switch to Classic View and restart Thunderbird. (see 531397)
Unresolved - Running TB 12 with local mail folders and pop3 mail filters may produce summary files that aren't correctly read by previous versions of Thunderbird. If you decide to go back to a previous version of Thunderbird after running TB 12, you should delete the .msf files for your local folders and pop3 accounts, or repair the folders using the folder properties dialog, to avoid potential data loss.