Thunderbird moves out
We have concluded that we should find a new, separate organizational setting for Thunderbird; one that allows the Thunderbird community to determine its own destiny.
Mozilla is currently only focused on Firefox:
Thunderbird effort is dwarfed by the enormous energy and community focused on the web, Firefox and the ecosystem around it. As a result, Mozilla doesn't focus on Thunderbird as much as we do browsing and Firefox and we don't expect this to change in the foreseeable future.