title: Firefox general.useragent.override not working
body: <p>to do some testings I have set the browser version for firefox by setting general.useragent.override="Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.1; Trident/4.0)" but the browser is still identified as Netscape not as IE.</p>
  
  <p>E.g. this JavaScript</p>
  
  <pre><code>console.log(navigator.appName);
  </code></pre>
  
  <p>still shows Netscape not IE as needed for the test. Any idea how to properely set the user agent in Firefox ?</p>