Firefox "Quantum" 57 dropped the support for legacy XUL addons and made WebExtensions the new standard for addon development inside the browser. For a project I built a WebExtension with multiple features which I'd like to share - it might help you!
Last year, in 2016, the people behind the Telegram messenger opened up a lot of features of their platform for developers. The so called "Bot API" makes it possible to connect to the Telegram servers, receive messages and communicate with the other clients inside the network. I was curious and developed a bot that has some use case if you are visiting our local library.