CVE-2026-74986: Site isolation issue in the CSS Parsing and Computation component

Affected Software

Remediation

Recommended actions to resolve this vulnerability, in priority order.

1. Upgrade

   Upgrade to a fixed release to a version that resolves this vulnerability.

   Fixed in 154
2. Upgrade

   Upgrade to a fixed release to a version that resolves this vulnerability.

   Fixed in 153.1
3. Upgrade

   Upgrade Mozilla Firefox / Firefox ESR / Thunderbird to a version that resolves this vulnerability.

   Fixed in 154
4. Upgrade

   Upgrade Mozilla Firefox ESR / Thunderbird ESR to a version that resolves this vulnerability.

   Fixed in 153.1

Event History

Parent advisories

This vulnerability appears in the following advisories.

• MFSA2026-74
• MFSA2026-77
• MFSA2026-80
• MFSA2026-78

Peer vulnerabilities

Found alongside the following vulnerabilities.

• CVE-2026-75874
• CVE-2026-74934
• CVE-2026-74935
• CVE-2026-74936
• CVE-2026-74937
• CVE-2026-74938
• CVE-2026-74939
• CVE-2026-74940
• CVE-2026-74941
• CVE-2026-74942
• CVE-2026-74943
• CVE-2026-74944
• CVE-2026-74945
• CVE-2026-74946
• CVE-2026-74947
• CVE-2026-74948
• CVE-2026-74949
• CVE-2026-74950
• CVE-2026-74951
• CVE-2026-74952
• CVE-2026-74953
• CVE-2026-74954
• CVE-2026-74955
• CVE-2026-74956
• CVE-2026-74957
• CVE-2026-74958
• CVE-2026-74959
• CVE-2026-74960
• CVE-2026-74961
• CVE-2026-74962
• CVE-2026-74963
• CVE-2026-74964
• CVE-2026-74965
• CVE-2026-74966
• CVE-2026-74967
• CVE-2026-74968
• CVE-2026-74969
• CVE-2026-74970
• CVE-2026-74971
• CVE-2026-74972
• CVE-2026-74973
• CVE-2026-74974
• CVE-2026-74975
• CVE-2026-74976
• CVE-2026-74977
• CVE-2026-74978
• CVE-2026-74979
• CVE-2026-74980
• CVE-2026-74981
• CVE-2026-74982
• CVE-2026-74983
• CVE-2026-74984
• CVE-2026-74985
• CVE-2026-74986
• CVE-2026-74987
• CVE-2026-74988
• CVE-2026-74989
• CVE-2026-74990
• CVE-2026-84637

Frequently Asked Questions