A race condition could have led to private browsing tabs being opened in normal browsing windows. This could have resulted in a potential privacy leak. This vulnerability affects Firefox < 135, Firefox ESR < 128.7, Thunderbird < 128.7, and Thunderbird < 135.
https://www.mozilla.org/security/advisories/mfsa2025-11/
https://www.mozilla.org/security/advisories/mfsa2025-10/
https://www.mozilla.org/security/advisories/mfsa2025-09/