ド素人に絡まれた件
作者かな


(function() {
  const PATTERN = {
    __proto__: null,
    'うんこ': 'XXX',
    'ウンコ': '排泄物'
  };
  const PATTERN_SHORTCUT = RegExp([x for (x in PATTERN)].join('|'));

  replace(document);

  document.addEventListener('DOMNodeInserted', function(event) {
    replace(event.target);
  }, false);

  function replace(target) {
    target.normalize();
    var x = document.evaluate('descendant::text()', target, null, 6, null);
    for (var i = 0, len = x.snapshotLength; i < len; i++) {
      var textNode = x.snapshotItem(i);
      textNode.nodeValue = textNode.nodeValue.replace(PATTERN_SHORTCUT, function($0) PATTERN[$0]);
    }
  }
})();