@julian Yeah, the images appear in a folder on their github, and I think they're referenced similar to how the nodebb emoji plugin works, but just has more cases to look out for.
I know this is quite old, but i encountered the same problem. I had localhost written in my config.json, but changed it to my domain. I still get GET http://localhost:4567/plugins/nodebb-plugin-emoji-extended/images/smile.png net::ERR_CONNECTION_REFUSED
I also restarted my server with the admin gui - is a hard restart or reinstallation necessary for the changes to take effect?