Yesterday many Firefox users woke up with a browser with no add-ons after Mozilla forgot to renew the security certificate that is used to sign Firefox add-ons.
The certificate expired causing new add-ons to fail and is stopping the existing add-ons from working.
Mozilla used an optional update channel called Studies to push out a hotfix but promised a more permanent fix.
That fix is Firefox 66.0.4 that has been approved as a Release candidate.
The update will bring “Repaired certificate chain to re-enable webextensions that had been disabled.”
The update may take a while to roll out, but eager users can download the update directly when it becomes available.