Sorry, the message you are seeing in your Firefox is not accurate. Your Firefox identifies itself as veresion 66.0.3, and almost certainly the add-ons are okay, but: A critical Add-on-related certificate expired (which obviously should not happen). As a result, all verifications for that certificate are failing, preventing many extensions from being used, updated, or installed. The Add-ons team is working on a fix for this. Official updates are expected to be posted here: https://discourse.mozilla.org/t/certificate-issue-causing-add-ons-to-be-disabled-or-fail-to-install/39047 Currently, the only workaround is to set your system clock back (for example, if your date is May 3, set to May 2; if your date is May 4, set to May 3). You might have to reinstall extensions after that, or maybe Firefox will detect the difference at your next shut down/restart. Changing the date may have other consequences, so I understand this option isn't ideal.

Brilliant! Thank you for the rapid and reassuring response!