Gasoline and Styrofoam doesn't create the substance Napalm, as the chemical combination lacks naphthene or palmitate. Napalm is just the broader term that the US Army applies to Weaponized Jellied Gasoline, which was petrol + benzene (already in gasoline) + polystyrene.

To make true original napalm (which was used up until Vietnam) you would need aluminum soap powder of napthenic and palmitic acids, hence (NA-PALM), that is the stuff that was originally in flamethrowers and incendiary bombs.