javascript: (function () {
  var elements = document.body.getElementsByTagName('*');
  var items = [];
  for (var i = 0; i < elements.length; i++) {
    if (
      elements[i].innerHTML.indexOf('html * { outline: 1px solid red }') != -1
    ) {
      items.push(elements[i]);
    }
  }
  if (items.length > 0) {
    for (var i = 0; i < items.length; i++) {
      items[i].innerHTML = '';
    }
  } else {
    document.body.innerHTML +=
      '<style>html * { outline: 1px solid red }</style>';
  }
})();


​