During operations on MessageTasks, a task may have been removed while it was still scheduled, resulting in memory corruption and a potentially exploitable crash. This vulnerability affects Thunderbird < 78.15, Thunderbird < 91.2, Firefox ESR < 91.2, Firefox ESR < 78.15, and Firefox < 93.
https://www.mozilla.org/security/advisories/mfsa2021-47/
https://www.mozilla.org/security/advisories/mfsa2021-46/
https://www.mozilla.org/security/advisories/mfsa2021-45/
https://www.mozilla.org/security/advisories/mfsa2021-44/
https://www.mozilla.org/security/advisories/mfsa2021-43/
https://www.debian.org/security/2022/dsa-5034
https://lists.debian.org/debian-lts-announce/2022/01/msg00001.html