Three security fixes, all listed as critical, address an integer overflow that caused crashes in the libtheora video library, a memory safety issue in the liboggplay media library, and crashes caused by memory corruption.
There were also changes made to the in-house upgrade from Thunderbird 2. Thunderbird 3 was released last December, but many users encountered problems including data loss and functionality bugs when upgrading. This fix released today addresses Mac users only, and prevents the e-mail client from deleting the contents of local trash sub-folders during the upgrade procedure.
The way that Thunderbird handles IMAP was also improved, as fixes were implemented for memory leaks and e-mails falsely marked as unread. The full change log can be read here.