messenger-blink.user.js

// ==UserScript==
// @name           messenger.com - No title blinking
// @namespace      
// @description    Disables page title blinking on messenger.com
// @include        https://www.messenger.com/t/*
// @copyright      Scott Zeid
// @version        1.0
// @grant          unsafeWindow
// ==/UserScript==

////////////////////////////////////////////////////////////////////////////////

function placebo() {};

var interval = setInterval(function() {
 var require = unsafeWindow.eval("require");
 if (require) {
  var dt = require("DocumentTitle");
  if (dt) {
   if (unsafeWindow.eval("require('DocumentTitle').blink.name") == "placebo") {
    clearInterval(interval);
    window.console.log("replaced DocumentTitle.blink()");
   }
   dt.blink = placebo;
  }
 }
}, 500);