title: Firefox extension opening a page on install
body: <p>I noticed some Firefox extensions when installed will open up a page once you restart the browser, for example the <a href="https://addons.mozilla.org/en-US/firefox/addon/138" rel="nofollow noreferrer">StumbleUpon toolbar</a>.</p>
  
  <p>This is useful to show update notes and give the user some tutorial type information.</p>
  
  <p>How do you go about opening a new page in a Firefox add-on the first time the user restarts the browser after install?</p>