JIT miscompilation in the DOM: Core & HTML component. This vulnerability was fixed in Firefox 152, Firefox ESR 140.12, Firefox ESR 115.37, Thunderbird 152, and Thunderbird 140.12.
https://www.mozilla.org/security/advisories/mfsa2026-61/
https://www.mozilla.org/security/advisories/mfsa2026-60/
https://www.mozilla.org/security/advisories/mfsa2026-59/
https://www.mozilla.org/security/advisories/mfsa2026-58/
https://www.mozilla.org/security/advisories/mfsa2026-57/
https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-12299.json
https://bugzilla.redhat.com/show_bug.cgi?id=2489212
https://bugzilla.mozilla.org/show_bug.cgi?id=2043139
https://access.redhat.com/security/cve/CVE-2026-12299
https://access.redhat.com/errata/RHSA-2026:33445
https://access.redhat.com/errata/RHSA-2026:30846
https://access.redhat.com/errata/RHSA-2026:29940
https://access.redhat.com/errata/RHSA-2026:27734