By injecting a cookie with certain special characters, an attacker on a shared subdomain which is not a secure context could set and thus overwrite cookies from a secure context, leading to session fixation and other attacks. This vulnerability affects Firefox ESR < 102.3, Thunderbird < 102.3, and Firefox < 105.
https://bugzilla.mozilla.org/show_bug.cgi?id=1779993
https://www.mozilla.org/security/advisories/mfsa2022-40/