The release notes, found here, list the changes to date. Some of these include:
- New Search with Advanced Filtering Tools
Search results now include advanced filtering tools. You have the option to filter your results by sender, tag, attachments, people, folder, and mailing list. You can also filter your email using the timeline tool.
- New Global Search Field with Autocomplete
When typing in the Global Search field, Thunderbird autocompletes against your address book. You have the option of searching everywhere or filtering against different parts of the email such as by subject or by sender.
- 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 Add-ons Manager
The new Add-ons Manager (Tools > Add-ons) can now be used to find, download, and install Thunderbird Add-ons which includes Extensions, Themes, and Plugins. Note that few Add-ons are compatible with this beta at the time of release, as Add-on developers need to upgrade them.
- IMAP Folder Synchronization
Thunderbird will download IMAP messages by default in the background to allow for faster message loading and better offline operation. This feature can be enabled on an individual folder basis via Folder properties, or for all folders in an account via Account Settings / ‘Synchronize & Storage’.
Of course, this is only a brief selection of some of the changes made to this new version of Thunderbird. Lifehacker has noted some more of the changes, showing off the search filtering, and said that Thunderbird 3.0 identifies people who participated in emails, by using your search terms, and promptly shows them all under a ‘People’ sidebar at the side, so you know who was involved. If you’d like to install version 3.0 of Thunderbird, please use the download links from this page, which we have included below (in U.S. English).