When performing add-on updates, certificate chains terminating in non-built-in-roots were rejected (even if they were legitimately added by an administrator.) This could have caused add-ons to become out-of-date silently without notification to the user. This vulnerability affects Firefox ESR < 68.10, Firefox < 78, and Thunderbird < 68.10.0.
https://www.mozilla.org/security/advisories/mfsa2020-26/
https://www.mozilla.org/security/advisories/mfsa2020-25/
https://www.mozilla.org/security/advisories/mfsa2020-24/
https://usn.ubuntu.com/4421-1/
https://security.gentoo.org/glsa/202007-10