If you let context2d() handle the scaling of the canvas, you must call ctx.resetTransform() before .drawImage(). I also recommend to always set ctx.canvas.style.maxWidth = '100%'

If you don't have a HiDPI display available, you can still emulate the behavior by passing a value > 1 as third argument to context2d()

For the record, none of these things fix the drawing behavior on my Linux FF machine. I guess it's one of those Canvas API inconsistencies that enables fingerprinting