title: How can I use window.history.pushState 'safely'
body: <p>I would like to use the <code>window.history.pushState()</code> function in supporting browsers. Unfortunately I'm getting an error on Firefox:</p>
  
  <blockquote>
    <p>TypeError: history.pushState is not a function</p>
  </blockquote>
  
  <p>How is it possible to avoid that?</p>