Those who use the latest version of Firefox (66.6) may have noticed that their usual extensions have disappeared. This is due to a bug in this browser in which an expired certificate gives the impression that all of these add-ons are corrupt. Mozilla has stated that a fix is being rolled out at present.
https://www.notebookcheck.net/Firefox-affected-by-bug-that-disables-all-the-browser-s-extensions.420157.0.html