screenshot mochitest

gistfile1.txt

function screenshot(win) {
  let canvas = win.document.createElementNS("http://www.w3.org/1999/xhtml", "canvas");
  let width = win.innerWidth;
  let height = win.innerHeight;
  canvas.mozOpaque = true;
  canvas.width = width;
  canvas.height = height;
  let ctx = canvas.getContext("2d");
  ctx.drawWindow(win, win.scrollX, win.scrollY, width, height, "#fff");
  info("Screenshot:" + canvas.toDataURL());
}