You can swipe left and right

[read about this feature being removed on 4/4/21]

When in popup puzzle view, you can swipe left and right instead of clicking the next and previous buttons at the top of the popup. As long as the next and previous buttons exist on the screen, swiping will trigger those buttons no matter where on the screen you swipe. This might make it easier to move from puzzle to puzzle when using touch devices. It also works with a mouse, but it isn't quite as natural feeling.