ComicSansKiller.js

// ==UserScript==
// @name        Comic Sans Killer
// @namespace   tw.walter.comicsanskiller
// @version     1
// @grant       none
// ==/UserScript==
/*
 * Comic Sans Killer
 * by Théophile Walter
 *    https://walter.tw
 */

removeComicSans(document.body, true);

function removeComicSans(d, mark) {
  // Browse child nodes
  var child = d.childNodes;
  for (var i = 0; i < child.length; i++) {
    // If Comic Sans
    if (typeof child[i].tagName != 'undefined' && isComicSans(child[i])) {
      // Remove and mark it
      child[i].style.fontFamily = 'Arial';
      if (mark && child[i].innerHTML != '') child[i].innerHTML += '&nbsp;<img src="https://walter.tw/cloud/file/fcb0e47daebe2a89a4bcc166e1f07792/cskilled.png" alt="[CSKilled]" style="width:1em;height:1em;display:inline;" />';
      // Browse child's child without mark (ovoid double marking for child)
      removeComicSans(child[i], false);
    } else {
      // Browse child's child with mark
      removeComicSans(child[i], true);
    }
  }
}

function isComicSans(el) {
  return css(el, 'font-family').toLowerCase().indexOf('comic sans') != - 1;
}

function css(element, property) {
  return window.getComputedStyle(element, null).getPropertyValue(property);
}