testing_hidden_visible_state.html

<!doctype html>
<script>
  window.onload = function(){
    window.setInterval(checkDocumentHidden,1000);
  };
  
  function checkDocumentHidden(){
    const ul = document.getElementById('states');
    let li = document.createElement('li');
    li.innerHTML = `document.hidden = ${document.hidden} document.visibilityState: ${document.visibilityState}`;
    ul.appendChild(li);
  
  }
</script>

<h1>Bug 1678103</h1>
  <div id="content">
    <ul id="states"></ul>
  </div>