A very useful tool for people who want to customise their YouTube experience.
It has been available for most browsers since about 2014, (I could be wrong about this, but it has been there for at least eight years.)
The developer is one of the few who actually listens to users' requests. Thus he almost always develops and implements functionality requested by real users.
One last thing;
In spite of the unpredictability of YouTube's proprietors (Google), who have changed everything multiple times, this developer has always been ahead of the game, and still is to this very day.