A race during concurrent delazification could have led to a use-after-free. This vulnerability affects Firefox < 135, Firefox ESR < 115.20, Firefox ESR < 128.7, Thunderbird < 128.7, and Thunderbird < 135.CreditsNils BarsReferenceshttps://bugzilla.mozilla.org/show_bug.cgi?id=1939710https://www.mozilla.org/security/advisories/mfsa2025-07/https://www.mozilla.org/security/advisories/mfsa2025-08/https://www.mozilla.org/security/advisories/mfsa2025-09/https://www.mozilla.org/security/advisories/mfsa2025-10/https://www.mozilla.org/security/advisories/mfsa2025-11/