On the Felixstowe F.5 and American F5L), those vertical structures sticking on top of the upper wings are aerodynamic balances for the ailerons. Specifically, they are horn-balanced ailerons (or inverse/overhung balances).
Because the Felixstowe F.5 was a massive, heavy flying boat with an immense wingspan, the aerodynamic forces acting on the wing's control surfaces were incredibly strong. Without physical assistance before boosted controls, it would require superhuman strength for a pilot to turn the control wheel and roll the aircraft.
The vertical panels extend upward past the hinge line of the aileron. When the pilot deflects the aileron downward, this vertical panel rotates into the oncoming airflow in the opposite direction via the visible horns and wires. The rushing wind pushes against the vertical panel, acting like a vane that naturally "helps" push the aileron into place, significantly reducing the physical force needed at the cockpit controls.
