<!DOCTYPE html>
<html>
  <head>
    <style>
      span {
        color: transparent; /* workaround for bug 617524 */
        outline: 1px solid green;
      }
    </style>
  </head>
  <body>
    <input><span>hide me</span>
    <input readonly>
    <input type=password><span>hide me</span>
    <input type=password readonly>
    <input type=email><span>hide me</span>
    <input type=email readonly>
    <textarea></textarea><span>hide me</span>
    <textarea readonly></textarea>
  </body>
</html>