title: Prevent Firefox from opening Privacy Notice when running web-ext?
body: <p>When developing web extensions, I test them with (for example) <code>web-ext run --bc -u https://stackoverflow.com/</code>.  With Firefox 56.0 (and <code>web-ext</code> 2.2.2), this:</p>
  
  <ol>
  <li>opens a window "Browser Console",</li>
  <li>opens another window and starts to load <a href="https://stackoverflow.com/">https://stackoverflow.com/</a> there, and</li>
  <li>opens another tab in that window to display the <a href="https://www.mozilla.org/en-US/privacy/firefox/" rel="nofollow noreferrer">Firefox Privacy Notice</a>.</li>
  </ol>
  
  <p>The last part is not only annoying in itself, but also distracting as (AFAICT) it fills the browser console with warnings related to that page's scripts.</p>
  
  <p>How can I prevent Firefox from opening the Firefox Privacy Notice when called from <code>web-ext</code>, perhaps by setting some preference with <code>--pref</code>?</p>