An attacker could have injected CSS into stylesheets accessible via internal URIs, such as resource:, and in doing so bypass a page's Content Security Policy. This vulnerability affects Firefox ESR < 91.11, Thunderbird < 102, Thunderbird < 91.11, and Firefox < 101.
https://www.mozilla.org/security/advisories/mfsa2022-20/
https://bugzilla.mozilla.org/show_bug.cgi?id=1757604