I will look into this.
THE DIFFERENCE IS THE FOLLOWINGT
SKULL CRUSHERS HAVE THE HUMERUS PERPENDICULAR TO THE FLOOR, THAT MEANS THERE WILL BE A REST AT THE TOP WHERE THE MUSCLES RELAX AS IN A LOCK OUT
FRENCH CURL HAS THE HUMERUS IN AN ANGLE TOWARDS THE HEAD MEANING THE BARBELL GOES NOT TO THE FOREHEAD BUT MORE TO THE CROWN OF THE HEAD AND AT THE TOP OF THE MOVE THERE IS NO RELAXATION BECAUSE THE WRISTS ARE NOT IN THE VERTICAL PLANE OF THE ELBOWS SO THERE IS A CONSTANT TENSION