So yesterday, at midnight UTC (9pm for me in eastern US), nearly all Firefox users had their add-ons and extensions disabled. And it was a mess. I followed a Reddit thread (there are a lot of them now) then switched to a Bugzilla bug thread. Through those, I learned I could download the “Nightly” version of Firefox and it would work.
It mostly didn’t. Neither did the other suggestions (such as going into about:debugging).
During the night, the Bugzilla crew came up with a fix BUT you have to have something turned in in the preferences. I’m still using the Nightly FF and it worked.
Go to Options
Go to Privacy and Security
Scroll to Firefox Data Collection and Use
Ensure you have the “Allow Firefox to send…” and the “Allow Firefox to install…” checked.
Go to Add-Ons. Wait a few seconds. You should see your add-ons/extensions start to move back to active. If the icon for one isn’t appearing at the top of the browser where it should be, disable then re-enable it. It should appear then.