This addon should be baseline to Firefox, it's so simple and yet you won't realise you need it until it's gone. I switched to Firefox from Chrome recently and one feature that I really miss is being able to mute all tabs from specific sites. It's a tiny but handy quality of life feature, and MuteLinks improves on Chrome's built-in muter. The ability to change between whitelist and blacklist modes, and the optional right-click context menu, are both very useful features.