# run this script on KiPython, the terminal embedded in PCB Editor
import pcbnew
visibility = False # change here to the visibility that you want to set
board = pcbnew.GetBoard()
footprints = board.Footprints()
for fp in footprints: # note: no more completion occur below loop...
    ref = fp.Reference()
    ref.SetVisible(visibility)
    #
    # type enter for 2 times
# Close the PCB and open again to see the result