title: firefox specify current window to stream with getUserMedia
body: <p>In firefox, I'm able to request a video stream of a window with</p>
  
  <pre><code>navigator.mediaDevices.getUserMedia({
      video: {
        mediaSource: 'window',
      },
  })
  </code></pre>
  
  <p>This produces a dialog like this: </p>
  
  <p><img src="https://trello-attachments.s3.amazonaws.com/58d428743111af1d0a20cf28/59f772aef52b867f0fd20f00/7394a0e9d832bbf15b5b2e4e3794fc84/capture.png" alt=""></p>
  
  <p>I only care about the current window. Is there a way to specify in my call to <code>getUserMedia</code> that I would like the current tab (or window) only?</p>