title: <canvas> in greasemonkey
body: <p>I've created a <code>&lt;canvas&gt;</code>, in the variable <code>canvas</code>, but I can't seem to draw to it. I can see the blank canvas on the page, but it's blank.</p>
  
  <pre><code>alert(ctx);
  ctx.fillStyle = "rgb(50,50,50)";
  ctx.fillRect(10,10, 55,50);
  alert("done");
  </code></pre>
  
  <p>The first alert says <code>[object CanvasRenderingContext2D]</code>, and I do see the "done" alert, but the canvas is still blank. There are no relevant errors in the error console.</p>
  
  <p>edit: Just to make sure, I pasted the script into a stand alone html page, and it worked as expected.</p>