title: Firebase notification not received behind proxy
body: <p>Does Firebase not work behind proxies?</p>
  
  <p>I am making an Android app for the students of my institute.
  The app does not receive the notification when it is connected to the internet through the proxy servers.</p>
  
  <p>But as soon as I turn on the mobile data, notifications are received.</p>
  
  <p>How do I solve this problem?</p>