You would probably have to drop it off of the empire state building to even possibly have a discharge from a floating firing pin. It just simply is not going to happen.
This is only a problem is semi autos, which move the bolt faster than you could ever hope to operate it. Even then it is very very rare.
I would not worry about it. My mini 14 has a floating firing pin and it doesn't slam fire.
EDIT- I just check, my moss berg 500 also has a floating firing pin and it is only maybe two years old at the most, which makes me believe all mossberg 500's have floating firing pins.
There is no such thing as a stupid question, only stupid people.