This is a problem with an expired intermediate certificate that is used to verify signed extensions that causes extensions to get disabled. This is being worked on.

See also:

• https://www.reddit.com/r/mozilla/comments/bkhjms/yes_firefox_has_disabled_many_extensions_no_its/

• https://discourse.mozilla.org/t/certificate-issue-causing-add-ons-to-be-disabled-or-fail-to-install/39047

At about 6:10 PST we received a report that a certificate issue for Firefox is causing add-ons to stop working and add-on installs to fail.
Our team is actively working on a fix. We will update as soon as we have more information.

• Bug 1548973 - (armagadd-on-2.0) All extensions disabled due to expiration of intermediate signing cert

(please do not comment in bug reports
https://bugzilla.mozilla.org/page.cgi?id=etiquette.html)

Firefox 66.0.3 came out a few weeks ago, but if you are posting because of a new problem with none of your add-ons working, starting at some point in the last 6 hours:

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. So it's not your connection; it's everyone's connection.

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 for the regular release of Firefox 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.

Thank You for your prompt reply and consideration.

Mozilla has rolled-out a fix for this. The fix will be automatically applied in the background within the next few hours, you don’t need to take active steps.

In order to be able to provide this fix on short notice, they are using the Studies system. You can check if you have studies enabled

1. Go to [=] > Options > Privacy & Security.
2. Make sure Allow Firefox to install and run studies is check marked.

I you had it disabled, you can disable studies again after your add-ons have been re-enabled.

They are working on a general fix that doesn't need to rely on this and will keep you updated.

Note that the hotfix is currently applied via a shield study, so you only get this fix when studies are enabled.

See also:

• https://blog.mozilla.org/addons/2019/05/04/update-regarding-add-ons-in-firefox/