So, does anyone use Thunderbird here?
Release Notes: https://www.mozillamessaging.com/en-US/thunderbird/5.0b1/releasenotes/
Interesting - thing is - it's still at 3.1.10 - I know Firefox has the 5.0 beta, the 6.0 alpha, and the 7.0 Nightly build - but I haven't seen a 4.0 of Thunderbird at all.