I used this Chrome extension for years and I absolutely loved it, and I'm so happy to see that it's available for Firefox as well! No other speed control addons are as simple or intuitive as this one. Highly recommend.

Better than other, seems without bugs ! thank you!

Basically the best add-on to control videos' speed on YT. Easy and intuitive. You can map your own shortcuts for keyboard (+ to increase, - to decrease, * to return at 1.00x) or simply adjust it with your mouse. You can also custom the increase and decrease speed.