YT_SideBar_Sticky.user.js

// ==UserScript==
// @name         YouTube Sidebar Sticky
// @namespace    https://gist.github.com/Wosser1sProductions/
// @version      0.1
// @description  Prevent side-bar from closing on click.
// @author       Wosser1sProductions
// @include      http*://*.youtube.com/*
// @include      http*://youtube.com/*
// @include      http*://*.youtu.be/*
// @include      http*://youtu.be/*
// @exclude      http*://*.youtube.com/watch*
// @grant        none
// ==/UserScript==

(function() {
    'use strict';

    var D = document;
    var root = D.documentElement;

    function getDocHeight() {
        return Math.max(
            D.body.scrollHeight, root.scrollHeight,
            D.body.offsetHeight, root.offsetHeight,
            D.body.clientHeight, root.clientHeight
        );
    }

    function getDocWidth() {
        return Math.max(
            D.body.scrollWidth, root.scrollWidth,
            D.body.offsetWidth, root.offsetWidth,
            D.body.clientWidth, root.clientWidth
        );
    }

    function stickSidebar() {
        if (!root.classList.contains("show-guide"))
            if ((document.body.scrollTop + 1200) < getDocHeight() && getDocWidth() > 1734)
                root.className += ' show-guide';
    }

    if (root.addEventListener) {                 // For all major browsers, except IE 8 and earlier
        root.addEventListener("mousemove", stickSidebar);
    } else if (x.attachEvent) {                  // For IE 8 and earlier versions
        root.attachEvent("mousemove", stickSidebar);
    }
})();