See the discussions that took place here:
Since the problem was related to a server certificate expiring, this hit everyone unexpectedly regardless of version as Firefox couldn't connect to Mozilla's server to prove extensions were legitimate or not (known as code signing).
It's been fixed, and no update is necessary as this was a problem on the server, but it did cause Firefox to disable extensions as a precaution. You may need to close Firefox entirely if extensions are still not loading for you.