Fun solitaire variant, especially once I figured out exactly how stacking on empty spaces worked. My strategy is to put cards/stacks in empty spaces only if doing so will free other cards that will lead to a new empty space as much as possible.

Everything runs smoothly in the browser. I think the only complaint I'd have is that all the face cards and the aces have the same picture, so I have to look harder at the written number to distinguish them (so sometimes I'll glance at the board and think there's an ace at the front when it's really something else)  

Edit after update: Aces now have different art! I'm still playing this game regularly, it's one of my favorites.