firefox is vulnerable to information disclosure. The MediaError message property could disclose confidential information about cross-origin resources.
bugzilla.mozilla.org/show_bug.cgi?id=1690976
lists.debian.org/debian-lts-announce/2021/03/msg00000.html
security-tracker.debian.org/tracker/CVE-2021-23973
security.gentoo.org/glsa/202104-09
security.gentoo.org/glsa/202104-10
www.debian.org/security/2021/dsa-4866
www.mozilla.org/en-US/security/advisories/mfsa2021-07/#CVE-2021-23973
www.mozilla.org/security/advisories/mfsa2021-07/
www.mozilla.org/security/advisories/mfsa2021-08/
www.mozilla.org/security/advisories/mfsa2021-09/