Before you ask, yes it is completely legal to ride your jet ski on the road in Florida.
As long as it is registered and has a visible tail light, you can take it out of the water and hit the streets. However, it is not very common to see someone actually do so.
This was quite the sight for one family in Jacksonville when they pulled up beside a jet ski driving in the lane next to them. As you can hear in the background, their child knows something is not right by shouting "that belongs in water!".
The driver was perfectly safe wearing both a helmet and protective eyewear and was just enjoying his afternoon drive.