title: fetch() fails in Firefox with SSL client authentication
body: <p>I have a web server which uses SSL client authentication. A web page on that server makes a same-origin <code>GET</code> request using the <code>fetch()</code> API.</p>
  
  <p>In Chrome, the client cert is sent in the SSL handshake, as expected, resulting in a 200 "ok" response. In Firefox, the cert isn't sent, resulting in a 403 "forbidden" response.</p>
  
  <p>In Firefox, if I switch it from using <code>fetch()</code> to <code>XMLHttpRequest</code>, it works. If I load the same URL directly from Firefox's URL bar, it works. The problem seems limited to <code>fetch()</code> on Firefox.</p>
  
  <p>Has anyone seen this before? Is there any way to make <code>fetch()</code> play well with SSL client auth in Firefox, or do I need to switch to using <code>XMLHttpRequest</code> everywhere? Thanks.</p>