There is a bug Mozilla is working on to fix.
You can get your extensions added (if missing) or enabled if you change an option in your Firefox browser. It is an option in your Firefox privacy setttings that allows or disallows Mozilla to collect data for “studies”. If you set it to allow the studies you can get your extensions back. Then you can reverse that setting when the bug is fixed.
it’s not owrking Wuli- at least not for firefox 57.04