Quote:The development team behind the email client Thunderbird released Thunderbird 60 in August 2018. Updates from Thunderbird 52.x to 60.x were not activated back then; users had to install Thunderbird 60 manually on their devices to run the upgrade.

Thunderbird 60 is a major release that introduced a number of important changes. The email client dropped support for the operating systems Windows XP and Windows Vista (and Server variants), made changes to the extensions system which blocked some extensions from running by default, and implemented a new design based on the Photon design of Firefox.

The team activated the Thunderbird 60 update this week. Thunderbird installations that are configured to check for updates automatically should pick up Thunderbird 60.3.0 eventually, the latest version available at the time of writing, and upgrade the email client to the new version automatically.

Thunderbird 60.3.0 is released as a staged update which means that the new version is not picked up by all clients automatically at once. Thunderbird users who want to upgrade right away need to select Help > About > Check for Updates to run a manual check for updates and install the new version.

Full reading: https://www.ghacks.net/2018/11/10/thunderbird-52-to-60-update-started/