Firefox has changed its addons framework and has completely switched to Web Extensions, just like chrome, opera and Edge. So legacy extensions won’t work anymore.
Since Greasemonkey is not a Web Extension so it won’t work now. You have to install some other extension which are supported by new firefox. Example extensions are:
- Tampermonkey (Tampermonkey – Get this Extension for 🦊 Firefox (en-US))
- VoilentMonkey (Violentmonkey – Get this Extension for 🦊 Firefox (en-US))
- USI (usi (User|Unified Script Injector) – Get this Extension for 🦊 Firefox (en-US))
Just install any one of these extenions and reinstall your scripts.