At the moment If you want to run a bleeding edge version of Thunderbird, you need to choose between running 3.2x and 3.1x builds. In fact, it appears that most people willing to run bleeding edge are now running 3.2x builds.
Whilst our most dedicated testers are running 3.2x builds, the engineering team is working on bringing features and bug fixes to the 3.1x branch. There’s a discrepancy here. This means that the issues that might exist in 3.1x have a greater chance to be discovered after releases rather than before. It’s easy to fix that, instead of running 3.2x builds, we would like our bleeding edge user to use the 3.1x builds (you can find them at http://ftp.mozilla.org/pub/mozilla.org/thunderbird/nightly/latest-comm-1.9.2/). By doing this simple switch you’ll help to make the 3.1 series a great series.