Removing an XSLT parameter during processing could have lead to an exploitable use-after-free. We have had reports of attacks in the wild abusing this flaw. This vulnerability affects Firefox < 97.0.2, Firefox ESR < 91.6.1, Firefox for Android < 97.3.0, Thunderbird < 91.6.2, and Focus < 97.3.0.
https://www.mandiant.com/resources/blog/zero-days-exploited-2022
https://www.tenable.com/cyber-exposure/tenable-2022-threat-landscape-report
https://www.mozilla.org/en-US/security/advisories/mfsa2022-09/