To harden ICU against exploitation, the behavior for out-of-memory conditions was changed to crash instead of attempt to continue. This vulnerability affects Firefox ESR < 115.9 and Thunderbird < 115.9.
https://www.mozilla.org/security/advisories/mfsa2024-14/
https://www.mozilla.org/security/advisories/mfsa2024-13/
https://lists.debian.org/debian-lts-announce/2024/03/msg00028.html
https://lists.debian.org/debian-lts-announce/2024/03/msg00022.html