Thunderbird 128.0, codenamed Nebula, introduces major changes to the program’s release cycle and code base. It will now follow a monthly-release cycle similar to Firefox, offering regular and ESR releases for users. Nebula brings significant code improvements, including a transition to Rust, aiming to enhance stability and user experience.

Users can expect a more responsive Thunderbird with better visual cues for navigation, including an organized context menu and improved Folder pane functionality. The program also boasts better integration with system themes, such as support for Ubuntu and Mint on Linux and native Windows notifications for Windows users. Additionally, Thunderbird now offers color cues in the From selection when composing new emails.

Despite these changes, existing users must download the installer to upgrade to the latest ESR release. Future updates will follow a monthly release schedule, with the ESR channel receiving bug and security fixes only.