Folk Physics

Let's test the intuitions today with one I gave to my first year seminar yesterday:

You are sitting in the aisle seat of a jet awaiting take-off when the child next to you hands you his helium balloon. You hold it in your hand next to the aisle as the plane taxis down the runway. During the taxiing, before take off, does the balloon move towards the back of the airplane, the front of the airplane, or float straight up?