Assuming a controlled failed memory allocation, an attacker could have caused a use-after-free, leading to a potentially exploitable crash. This vulnerability was fixed in Firefox 134, Firefox ESR 128.6, Firefox ESR 115.19, Thunderbird 134, and Thunderbird 128.6.
https://www.mozilla.org/security/advisories/mfsa2025-05/
https://www.mozilla.org/security/advisories/mfsa2025-04/
https://www.mozilla.org/security/advisories/mfsa2025-03/
https://www.mozilla.org/security/advisories/mfsa2025-02/
https://www.mozilla.org/security/advisories/mfsa2025-01/
https://lists.debian.org/debian-lts-announce/2025/01/msg00004.html