The WebAssembly JIT could miscalculate the size of a return type, which could lead to a null read and result in a crash. *Note: This issue only affected x86-32 platforms. Other platforms are unaffected.*. This vulnerability affects Firefox ESR < 78.10, Thunderbird < 78.10, and Firefox < 88.
https://www.mozilla.org/security/advisories/mfsa2021-16/
https://www.mozilla.org/security/advisories/mfsa2021-15/