Thunderbird 3.0.11 was the last security and stability update for
Thunderbird 3.0.x. Thunderbird 3.0.x users will be prompted and
encouraged to start using Thunderbird 3.1.
We strongly recommend that all Thunderbird users upgrade to this
release. If you already have Thunderbird 3.1, you will receive an
automated update notification within 24 to 48 hours. You can also
manually fetch this update by selecting “Check for Updates…” from the
Help menu.
For a list of changes and more information, please review the
Thunderbird 3.1.8 release notes:
http://www.mozillamessaging.com/en-US/thunderbird/3.1.8/releasenotes/