Navy Pier is open whenever they do fireworks (in my experience). It's a pretty boring place, fireworks or no fireworks IMO. Just go down to the end on the south side and there's lots of room.

I would agree that watching them from down by the Shedd Aquarium / Planetarium would be a better all around view though. ou will need to eat first and then make your way down there - unless you're goign to the museums there is nothing else there.