A new version of Thunderbird, version 2.0.0.23, is available.  Thus update fixes MFSA 2009-42 (Compromise of SSL-protected communication). 

If you are a Thunderbird user, it is probably best to apply this update as soon as convenient.

Update:

It appears this update, which affects multiple Mozilla products, has changed the rules for security certificates generated with wildcards. More information is available at the Fourmilab Blog.

-- Rick Wanner - rwanner at isc dot sans dot org