1) I changed line 44 of of filetype_extensions.conf to: `#~ Javascript=*.js;*.mjs;` 2) Saved the file 3) Closed Geany 4) Re-Launched Geany 5) Opened a file with `.mjs` file extension
Still, the `.mjs` file is not receiving Javascript highlighting. Maybe I didn't read the [manual](https://www.geany.org/manual/current/index.html#filetype-extensions) slow enough. I'm doing that now.