<script>
var myFunction = function(a){            // Supply a valid selector (e.g '*' for wildcard)
  [].forEach.call(                       // Treat Nodelist as an Array (fewer bytes than Array.prototype.forEach.call(...);)
                                         // Gets the prototype of Array & uses call to execute the function on the NodeList.
    document.querySelectorAll(a),        // Query DOM for elements matching the supplied selector
                                         // (For 110 bytes, use $$() as Chrome, Safari & FF expose it in DevTools)
    function(b){
      b.style.outline = "1px solid #" +  // Set the selector outline
      (~~(Math.random()*(1<<24)))       // Pick a valid random CSS hex color
      .toString(16)})                   // Convert to a base 16 number. BOOM.
}
  myFunction('*');
</script>