I recall something about this. Looked it up quickly and found this pretty sure it’s what they are referring to.
[FIXED] Certificate issue causing add-ons to be disabled or fail to install: May 5, 2019: We released Firefox 66.0.4 for Desktop and Android, as well as Firefox 60.6.2 ESR that re-enables extensions. For more information, please read the update on https://blog.mozilla.org/addons/2019/05/04/update-regarding-add-ons-in-firefox Thank you for being patient with us! Thanks to everyone working on it! May 14, 2019: If you are running Firefox 52 - 56 , you can install this extension to fix the expi...