Also vote here: https://www.change.org/p/no-add-on-signing-in-firefox

You’re welcome. Are you a LibreWolf developer?

afaik, only in tandem with search history

Great, I want that too.

and if you look for it on about:config, it’s enabled

The about:config setting has been placebo since version 48. It doesn’t affect anything.

Firefox 48: (Pushed from Firefox 46). Release and Beta versions of Firefox for Desktop will not allow unsigned extensions to be installed, with no override. Firefox for Android will enforce add-on signing, and will retain a preference — which will be removed in a future release — to allow the user to disable signing enforcement.

(source)