The ms-msdt, search, and search-ms protocols deliver content to Microsoft applications, bypassing the browser, when a user accepts prompt. These applications have had known vulnerabilities, exploited in wild (although we know of none through Thunderbird), so this release Thunderbird has blocked these from prompting open them.
*This bug only affects on Windows. Other operating systems are unaffected.*. This vulnerability Firefox < 102, ESR 91.11, 91.11.