Caprine is an unofficial and privacy focused Facebook Messenger app with many useful features. 
Built with Electron, Caprine features a Dark mode, keyboard shortcuts, ability to toggle last seen/typing indicators, work chat support, code blocks, custom text size, and an interface that adapts to resizing windows.

Caprine is a third-party app and is not affiliated with Facebook. 

To run: Menu -> Internet -> Caprine
To run in a terminal: /opt/Caprine/caprine