This repo is a template for custom JS scripts extension.
Feel free to clone it and add your own custom behaviours to websites.
Use the extension in unpacked format in order to use it in Google Chrome (app folder of the repo)
Firefox doesn't support unpacked extensions, so you'll have to distribute your extension in private mode if you're up for it. You'll have to update the extension manually after that; but you'll have a benefit of auto-update between your computers instead of manually doing git pull to sync your changes.
See the usage examples in app/index.js
You can also add global styles to app/styles/main.css.