Thunderbird 5.0 beta was released few days ago, and it has the following changes:

  • 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

    • Read release note)

A new created untrusted ppa provides packages of Thunderbird beta for Ubuntu Lucid, Karmic, and Natty. Use following commands adding this ppa and install Thunderbird 5 beta:

sudo add-apt-repository ppa:mozillateam/thunderbird-next
sudo apt-get update
sudo apt-get install thunderbird