Highlights a username in the chat in yellow if it's the first time they sent a message in your browser session, then adds them to a list of observed chatters and adds a mutationoberver to look for new chats.
// ==UserScript==
// @name Twitch.tv highlights first chats from users - Light mode
// @namespace https://greasyfork.org/users/1188705
// @version 1.0
// @description Highlights a username in the chat in yellow if it's the first time they sent a message in your browser session, then adds them to a list of observed chatters and adds a mutationoberver to look for new chats.
// @author sunmilk50
// @license public domain
// @match https://www.twitch.tv/*
// @grant none
// ==/UserScript==
(function(){const b=new Set;(new MutationObserver(function(e){e.forEach(function(c){"childList"===c.type&&Array.from(c.addedNodes).forEach(a=>{if(a.classList&&a.classList.contains("chat-line__message")){const d=a.querySelector(".chat-author__display-name").innerText;b.has(d)||(a.style.backgroundColor="yellow",b.add(d))}})})})).observe(document.body,{childList:!0,subtree:!0})})();