Multiple security issues have been found in Thunderbird, which may lead to the execution of arbitrary code or denial of service. Debian follows the Thunderbird upstream releases. Support for the 68.x series has ended, so starting with this update we"re now following the 78.x releases. The 78.x series discontinues support for some addons. Also, starting with 78, Thunderbird supports OpenPGP natively. If you are currently using the Enigmail addon for PGP, please refer to the included NEWS and README.Debian.gz files for information on how to migrate your keys.