Thunderbird 5.0 Beta 1

* New Addons Manager and extension management API (user interface will be changed before final release)
* Tabs can now be reordered and dragged to different windows
* Revised account creation wizard, offering improved set-up
* Attachment sizes now displayed along with attachments
* New troubleshooting information page to aid supporting and diagnosing problems in Thunderbird
* Plugins can now be loaded in RSS feeds by default
* Various other user interface fixes and improvements
* Support for Mac 32/64 bit Universal builds (Thunderbird Beta will no longer support PowerPC on Mac)
* and numerous other bug fixes