The Grid, Custom Zoom, and Dynamic Cursors
New: The Grid. Zoom to 4x+ and use View > Zoom > Show Grid or Ctrl+G to enable. This works with browser zoom as well to provide crisp gridlines even if you zoom in with your browser.
New: View > Zoom > Custom Zoom, including an actually-custom numerical zoom option, unlike MS Paint.
New: Dynamic cursors for brush and eraser, so you now have a preview of exactly where the tool will draw.
Also, in the event that your browser clears canvases to free up memory, you should be more likely to be able to undo to get back to a useful state.