This is a random collection of noteworthy issues that I happen to stumble over.
The installer deletes the directory 'distribution'.
Thunderbird is usually not available any more in both variants RR and ESR, because there is not much development going on. The normal version behaves like ESR because new features are only added with the version step that happens simultaneously with a new ESR version of Firefox.
Hovever for the 12 week period of versions 31 and 32 Mozilla offers Thunderbird versions 24.7 and 24.8, to give the former ESR users more time for the version switch.
Thunderbird 24.7 cannot be downloaded from the normal download page. Instead if can be found here:
Starting with version 24.7 it shows an error if the autoconfig file sets the pref "toolkit.telemetry.prompted" to true. It must now be set to 2.
The menu line is now shown higher than previously (if it is enabled). If you had enabled it with userChrome.css, this can cause it to be visible but inactive, meaning you cannot grab the window there to drag it. You should not use userChrome.css any more to enable the menu bar, there is now a better method: set the pref "mail.mail_menu.collapse_by_default" to false.
New features according to the release notes:
But this list is woefully incomplete.
Several more are here: http://news.softpedia.com/news/Mozilla-Thunderbird-31-What-s-New-451811.shtml
This should be the first version in which the auto-update through the updater service actually works. In all previous versions it worked only if Thunderbird is installed in a directory where the user has write access, or if the user actively triggered the update by clicking on one of the reminders.