When using Alt-Svc, ALPN did not properly validate certificates when the original server is redirecting to an insecure site. This vulnerability affects Firefox < 134, Firefox ESR < 128.6, Thunderbird < 134, and Thunderbird < 128.6.
https://www.mozilla.org/security/advisories/mfsa2025-05/
https://www.mozilla.org/security/advisories/mfsa2025-04/
https://www.mozilla.org/security/advisories/mfsa2025-02/
https://www.mozilla.org/security/advisories/mfsa2025-01/
https://lists.debian.org/debian-lts-announce/2025/01/msg00004.html