title: Offscreencanvas illegal constructor
body: <p>I'm testing the new <a href="https://developer.mozilla.org/en-US/docs/Web/API/OffscreenCanvas" rel="nofollow">offscreen Canvas in firefox</a>, and I haven't any trouble with asynchronous offscreen canvas in web workers (gfx.offscreencanvas are enabled), but when I try to do the first example, I get an illegal constructor error in offscreenCanvas constructor:</p>
  
  <pre><code>var offscreen = new OffscreenCanvas(256, 256);
  </code></pre>
  
  <p><a href="https://jsfiddle.net/meji/hrwp7ju4/" rel="nofollow">Here</a> an example. I'm using firefox 44 on ubuntu 15.10.</p>