title: XMLHttpRequest not sent
body: <p>We are three developers working on a web-app project with Django.</p>
  
  <p>Some communications client-server use an API. One particular request is not sending on one of the developer's computer. We use the same Browser (Firefox quantum 64.0 (64 bits)), same OS (Ubuntu 18.04).</p>
  
  <p>Here is the JS snippet:</p>
  
  <pre><code>function requestHandler(url){
      let xhttp = new XMLHttpRequest();
      xhttp.open('POST', url, true);
      xhttp.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded');
      xhttp.setRequestHeader('X-CSRFToken', getCookie('csrftoken'));
  
      xhttp.onreadystatechange = function(){
          if (this.readyState == 4 &amp;&amp; this.status == 200) {
              drawLogTable();
          }
          else if (this.readyState == 4){
              console.log(this);
              new PNotify({
                  title: 'Échec!',
                  text: "Opération impossible: " + this.statusText,
                  type: 'error'
              });
          }
      }
      xhttp.send();
  }
  </code></pre>
  
  <p>Note that <code>url</code> is <code>'../../api/log?action=accept&amp;id=1'</code></p>
  
  <p>On all the working computers and browsers, the request posts and does a 404 since server-side has no implementation yet. On the non-working computer, chromium works, but under Firefox, the request is not even sent (server log is empty) and the request object is completely empty (no status, no text).</p>
  
  <p>We have other AJAX requests in the same type that are working fine.</p>