У вашего броузера проблема в совместимости с HTML5
The error 502 Bad Gateway, also known as HTTP 502 Error is included inside the HTTP response status code. A website server is used as a proxy or gateway to serve the clients request. However, if the same proxy or gateway receives an invalid response from the server, then a HTTP 502 Bad Gateway Error is displayed. One of the causes of a HTTP 502 Bad Gateway Error is that both server and gateway have not reached an agreement on exchanging data.