I have released FireMonkey which uses the new secure userScript API in Firefox65+.
If you find it useful, you can list it as one of Firefox extensions for userScripts.
Firemonkey is a totally new extension that can handle both user Scripts and user CSS. While it has similar functions to user script extensions like GreaseMonkey, and user CSS extensions like Stylish or Stylus, there are differences. Similar to GreaseMonkey, scripts (or CSS) are injected in tabs and for a new script/CSS to have an effect, tab must be reloaded. The behaviour differs from Stylus which can inject CSS into a tab and remove it without having to reload the tab.
FireMonkey for Firefox 65+
I have released FireMonkey which uses the new secure userScript API in Firefox65+.
If you find it useful, you can list it as one of Firefox extensions for userScripts.