XSLT document loading did not correctly propagate the source document which bypassed its CSP. This vulnerability was fixed in Firefox 141, Firefox ESR 128.13, Firefox ESR 140.1, Thunderbird 141, Thunderbird 128.13, and Thunderbird 140.1.
https://www.mozilla.org/security/advisories/mfsa2025-63/
https://www.mozilla.org/security/advisories/mfsa2025-62/
https://www.mozilla.org/security/advisories/mfsa2025-61/
https://www.mozilla.org/security/advisories/mfsa2025-59/
https://www.mozilla.org/security/advisories/mfsa2025-58/
https://www.mozilla.org/security/advisories/mfsa2025-56/
https://lists.debian.org/debian-lts-announce/2025/07/msg00016.html