title: moment js diff function is failing in firefox and safari, but works fine in chrome
body: <p>I'm using moment.js diff function to calculate difference of days between two dates. It works fine in chrome, but in firefox and safari returning NaN.</p>
  
  <pre><code>const month = 05;
  const day = 05;
  const year = 1987;
  const date = new Date(year, month, day);
  const dob = moment(date).format('MM-DD-YYYY');
  const diff = moment().diff(dob, 'days', true);
  </code></pre>
  
  <p>the value of diff is correct in chrome, but returning NaN in firefox and safari.</p>
  
  <p>Any help please?</p>