I've been using Stylish for many years with Firefox to customize the user interface itself. It was very convenient. Unfortunately since FF57 manipulating the user interface is no longer supported via add-ons (have to do it manually through userChrome.css). This is of course not the developer's fault and this is still a very good add-on for what it does, but no longer useful to me I'm afraid. This is why I gave it only 4/5 stars.