title: SignalR with Firefox shows XML Parsing Error in console
body: <p>I am using signalr 2.2.2 in an MVC application. Everything works ok apart from the fact, that every time the application navigates to another page a console error in the following form is shown:</p>
  
  <pre><code>XML Parsing Error: no root element found
  Location: http://localhost/signalr/abort?transport=serverSentEvents&amp;clientProtocol=1.5&amp;connectionToken=2elX1XZHXH0xmQaLZKyHUFW5Z2rb2DGRYEI...
  </code></pre>
  
  <p>This only happens in firefox. Does anybody know how to fix this?
  Thanks</p>