The origin of an external protocol handler prompt could have been obscured using a data: URL within an `iframe`. This vulnerability affects Firefox < 132, Firefox ESR < 128.4, Thunderbird < 128.4, and Thunderbird < 132.
https://www.mozilla.org/security/advisories/mfsa2024-59/
https://www.mozilla.org/security/advisories/mfsa2024-58/
https://www.mozilla.org/security/advisories/mfsa2024-56/