<html>
<head>
  <script>
    function start () {
      const canvas = document.createElementNS('http://www.w3.org/1999/xhtml', 'canvas')
      SpecialPowers.forceGC();
      canvas.toBlob(function (blob) {
        blob.stream()
        blob.arrayBuffer().then(() => {})
      })
    }

    window.addEventListener('load', start)
  </script>
</head>
</html>
