Issues have been fixed in Thinderbird including arbitrary code execution, SSL tampering, memory corruption and same-origin violations when Flash loads. Some of these issues also affected Firefox and were fixed in version 3.0.11. If you or your organization is using Thunderbird as your mail application install update 2.0.0.22.
http://www.mozillamessaging.com/en-US/thunderbird/2.0.0.22/releasenotes/