mozilla-release/layout/reftests/forms/input/number/focus-handling.html

<!DOCTYPE html>
<html class="reftest-wait">
  <!-- In this case we're using reftest-wait to make sure the test doesn't         
       get snapshotted before it's been focused. We're not testing                 
       invalidation so we don't need to listen for MozReftestInvalidate.           
  -->                                                                              
  <head>
    <meta charset="utf-8">
    <script>

function begin() {
  setTimeout(function() {
    document.getElementsByTagName('input')[1].focus();
  }, 0);
}

function end() {
  setTimeout(function() {
    document.documentElement.className = "";
  }, 0);
}

    </script>
  </head>
  <body>
    <input type='number' autofocus onfocus="begin();"
           style="-moz-appearance:none;"><br>
    <input type='number' onfocus="end();"
           style="-moz-appearance:none;">
    <!-- div to cover spin box area for type=number to type=text comparison -->
    <div style="display:block; position:absolute; background-color:black; width:200px; height:100px; top:0px; left:100px;">
  </body>
</html>