A website could have obscured the fullscreen notification by using a dropdown select input element. This could have led to user confusion and possible spoofing attacks. This vulnerability affects Firefox < 123, Firefox ESR < 115.8, and Thunderbird < 115.8.
bugzilla.mozilla.org/show_bug.cgi?id=1832627
lists.debian.org/debian-lts-announce/2024/03/msg00000.html
lists.debian.org/debian-lts-announce/2024/03/msg00001.html
www.mozilla.org/security/advisories/mfsa2024-05/
www.mozilla.org/security/advisories/mfsa2024-06/
www.mozilla.org/security/advisories/mfsa2024-07/