Firefox 66.0.4 has been released to the Stable channel and contains a fix for the expired intermediate signing certificate that caused everyone’s addons to be disabled on Friday. Mozilla allowed an intermediate certificate to expire that is used to sign Firefox addons. As a temporary fix, Mozilla issued an extension through their Normandy Study system that installed a new intermediate signing. Once the hotfix was installed, addons would automatically be enabled again. Mozilla has now released a new certificate that is not expired and will force signature reverification.
Source: https://www.bleepingcomputer.com/news/software/firefox-6604-released-with-fix-for-disabled-addons/