There are a number of browser extensions I consider myself unable to live without.
The speed control extension that adds keybinds for changing speed and allows me to go beyond 2x still tops the list, but DeArrow is a very, very close second.
Its job is to fightclicknbait by allowing users to suggest alternate titles and thumbnails for videos and getting rid of words in ALL CAPS??!!????!?
Assuming you meant the video speed control extension, there are a number of them. Here's the exact one I use. I found it through the highly technical method of Googling "YouTube speed control extension", installing the first couple hits, picking the one I liked best, and uninstalling the others. I like this extension because it supports custom keybinds for speeding up/slowing down by arbitrary amounts and jumping to a preset speed, and because it works on all sites that play video, not just YouTube, meaning I can turn up the speed on Netflix if I want.