If a compromised content process sent an unexpected number of WebAuthN Extensions in a Register command to the parent process, an out of bounds write would have occurred leading to memory corruption and a potentially exploitable crash. This vulnerability affects Thunderbird < 91.8, Firefox < 99, and Firefox ESR < 91.8.
https://www.mozilla.org/security/advisories/mfsa2022-13/
https://bugzilla.mozilla.org/show_bug.cgi?id=1755621