YouTube SpeedUp by GoliafRS

Use YouTube SpeedUp by finding the speedometer button in the native YouTube player controls, then scrolling on it to increase or decrease playback speed. Click the button to reset speed to 1.00, or use Enter, Space, and the Arrow keys for keyboard control. Hovering the button shows the current speed, your saved speed is applied across YouTube navigation, and scrolling on the button also prevents the page from scrolling, including in fullscreen. When enabled, the same control also appears in YouTube Shorts.

You can open the settings page in Firefox through about:addons, then Extensions, then YouTube SpeedUp, then Options. In settings, you can enable the extension separately for regular videos and Shorts, set the saved playback speed, change the speed increment, or reset everything to the default values. All settings are stored locally in your browser, no data is collected, and the extension is designed for Firefox 140+ on desktop.