Thunderbird 3 Beta 3 is based on the Gecko 1.9.1.1 platform including some major
re-architecting to provide improved performance, stability, web compatibility,
and code simplification and sustainability.

There are over 500 changes in this release, many laying the groundwork for
future changes. Some notable changes include:


Developer Improvements

* Thread Pane and Tab Refactoring
* Fixes For Extension Developers


User Experience Improvements

* Tabbed Email Messages - Double-clicking or hitting enter on a mail message
will now open that message in a New Tab window. Middle-clicking on messages
or folders will open them in a Tab in the background. When quitting
Thunderbird, visible tabs will be saved and will be restored when you open
Thunderbird the next time. There is also a new Tab menu on the Tab toolbar
to help you switch between Tabs.

* New Message Summary View - Selecting multiple messages will give you a
summary view of the emails you have selected.

* Column Headings - The column headings that are displayed and the order in
which they are displayed can now be set on a per-folder basis.

* Smart Folders - The folder pane offers a Smart Folders mode which combines
special mailboxes (e.g. Inbox) from multiple accounts together.

* Improved Gmail Integration - Better recognition and integration of Gmail's
special folders such as Sent and Trash including non-English versions of
Gmail. Thunderbird also uses All Mail as the Archives folder.