Broken in Firefox due to missing Canvas2D ellipse method. I filed a bug in Bugzilla (https://bugzilla.mozilla.org/show_bug.cgi?id=1067039), but a quick fix would be replacing the ellipse with a rectangle.
A quick workaround is to run the following in the error console:
ctx.ellipse = function (x, y, radiusX, radiusY, rotation, startAngle, endAngle, anticlockwise) { ctx.arc(x, y, Math.max(radiusX, radiusY), rotation, startAngle, endAngle, anticlockwise); }