Persist FB volume

userscript.js

// ==UserScript==
// @name         Facebook video volume persistence
// @namespace    http://tampermonkey.net/
// @version      1.1
// @description  Maintains set volume of videos on play of videos on Facebook.
// @include      https://facebook.com/*
// @include      https://www.facebook.com/*
// @grant        GM_setValue
// @grant        GM_getValue
// ==/UserScript==

(function () {
  "use strict";
  var volume = 0.3;

  setInterval(() => {
    var videos = document.querySelectorAll('video');

    for (let video of videos) {
      video.addEventListener('play', (e) => {
        // console.log(e.target.volume);
        e.target.volume = volume;
        // console.log(volume);
      });
    }
  }, 1000);
})();