An attacker could have exploited a timing attack by sending a large number of allowCredential entries and detecting the difference between invalid key handles and cross-origin key handles. This could have led to cross-origin account linking in violation of WebAuthn goals. This vulnerability affects Thunderbird < 91.10, Firefox < 101, and Firefox ESR < 91.10.
https://www.mozilla.org/security/advisories/mfsa2022-22/
https://www.mozilla.org/security/advisories/mfsa2022-21/