For Windows, Mac and Linux: Thunderbird 3.0 Release Candidate 1 is now available for download, for all platforms. Most of the features in this release are already present in the beta releases liked Tabbed emails, New Search with Advanced Filtering Tools, message archiving, the Activity Manager and more. But Thunderbird 3 RC 1 also addresses stability issues, improves performance and web compatibility and simplifies code and sustainability.
To install Thunderbird 3 RC1 on your Ubuntu, follow this guide: A Single Command Install of Thunderbird 3 on Ubuntu
Download Thunderbird 3 Release Candidate 1, a preview release of the next major Thunderbird.