If you have friends that want to start with building WebExtensions show them this link https://vimeo.com/240282133
Most people start with “Hello World” web sites when they want to learn Front End stuff. This is boring. Building an WebExtension as the first web project is sooo totally awesome! 
I choose to sign it as unlisted WebExtension since lots of people don’t know it’s possible and if you are a n00b and want to share your extension in 5 minutes regardless of how useless it is, an unlisted web extension is better than a listed one.