Recently Mozilla changed to a quicker release system for Firefox, and Thunderbird was to follow suit. Today is its first delivery on that goal.
Since Firefox and Thunderbird share so much common technology (XULRunner) Thunderbird would have to adapt to the new model, but in order to keep things simple, they have synchronized the version number as well. So now after Thunderbird 3.0 and 3.1, we will get Thunderbird 5.0 — it's just a number, but we do feel like we have missed out on Thunderbird 4!
Thunderbird 5 beta come with a number of new features:
- An even better account creation wizard
- The new Firefox add-on manager
- Use of Aero glass effects on Thunderbird chrome on Windows
- Better attachment display with file sizes
- Tab reordering, tearing, and moving from one window to another
- RSS feeds now display plug-ins
There are numerous other small feature that you can find out about here.