Version 87.0, first offered to Release channel users on March 23, 2021
https://www.mozilla.org/en-US/firefox/87.0/releasenotes/
https://www.mozilla.org/en-US/firefox/all/#product-desktop-release
Firefox ESR 78.9.0 Release Notes - March 23, 2021
https://www.mozilla.org/en-US/firefox/78.9.0/releasenotes/
MFSA 2021-12 Security Vulnerabilities fixed in Thunderbird 78.9 - March 23, 2021
MFSA 2021-11 Security Vulnerabilities fixed in Firefox ESR 78.9 - March 23, 2021
MFSA 2021-10 Security Vulnerabilities fixed in Firefox 87 - March 23, 2021