https://blog.darkwood.fr/article/raccourci-pour-lire-des-videos-2x

fix-youtube-shortcut.user.js

// ==UserScript==
// @name         Youtube customisation
// @namespace    https://darkwood.fr
// @version      0.0.1
// @description  Create youtube specific actions
// @author       matyo91
// @match        https://*.youtube.com/*
// @compatible   firefox >=52
// @compatible   chrome >=55
// @license      MIT
// ==/UserScript==

// fix Youtube shortcut to speed down video for AZERTY keyboard
// detail : https://blog.darkwood.fr/article/raccourci-pour-lire-des-videos-2x

(function() {
    'use strict';

    var functions = {
        upPlaybackSpeed() {
            document.querySelector(".html5-video-player video").playbackRate = document.querySelector(".html5-video-player video").playbackRate + 0.1
        },
        increasePlaybackSpeed: function() {
            var player = document.querySelector('#movie_player');

            if (player && player.setPlaybackRate && player.getPlaybackRate) {
                player.setPlaybackRate(player.getPlaybackRate() + .1);
            }
        },
        decreasePlaybackSpeed: function() {
            var player = document.querySelector('#movie_player');

            if (player && player.setPlaybackRate && player.getPlaybackRate) {
                player.setPlaybackRate(player.getPlaybackRate() - .1);
            }
        },
        resetPlaybackSpeed: function() {
            var player = document.querySelector('#movie_player');

            if (player && player.setPlaybackRate && player.getPlaybackRate) {
                player.setPlaybackRate(1);
            }
        },
    }
    
    document.addEventListener("DOMContentLoaded", function() {
        window.addEventListener('keydown', function(event) {
            console.log(event.keyCode)
            if(event.keyCode === 188) { // '<'
                functions.resetPlaybackSpeed();
            }
        });
    });
})();