https://www.thunderbird.net/en-US/thunderbird/68.9.0/releasenotes/
https://www.mozilla.org/en-US/security/known-vulnerabilities/thunderbird/#thunderbird68.9 未更新
6/8 追記
Security Vulnerabilities fixed in Thunderbird 68.9.0 - Mozilla Foundation Security Advisory 2020-22
追記終わり