Thunderbird spun out to a separate corporation
The Thunderbird email client has been moved
into a separate company called "MZLA Technologies Corporation", which
remains wholly owned by the Mozilla Foundation. "Moving to MZLA Technologies Corporation will not only allow the Thunderbird project more flexibility and agility, but will also allow us to explore offering our users products and services that were not possible under the Mozilla Foundation. The move will allow the project to collect revenue through partnerships and non-charitable donations, which in turn can be used to cover the costs of new products and services.

Thunderbird’s focus isn’t going to change. We remain committed to creating
amazing, open source technology focused on open standards, user privacy,
and productive communication."