You should clone this repo and modify it for your needs, then
run zip.sh , add build.zip as "Load Temporary Add-on.." from
about:debugging#/runtime/this-firefox
The tool which gives your scripts superpowers and allows this addon to read scripts from your local system, is Http-Multi-Server - my other repo.
Obviously it needs to be running.
That way you can store scripts locally and manage them with syncthing or git or whichever way you like.
Your scripts may then also store local files or run shell scripts or do whatever the hell you want them to do.
Obviously this is only for your own scripts and not random scripts you get from the internet.