Some double rifles have floating firing pins and some do not. When properly set up floating pins can work as a pressure relief valve in the event of a blown primer. On a double other then one chambered for a low intensity cartridge I would prefer floating pins. One big pluss to the floating pins and a good part of the reason they were and still are used is the ease of replacing a broken pin.
Dogs toothed strikers, or tumblers,(where the firing pin is part of the hammer)can not be replaced in the field unless you bring the tools needed to take the action or locks down with you. Dogs toothed strikers do work for gas control on a box lock though not as well as the floating pins do. Gas blowing past the striker is directed down into the action and forward however this could mean a blown stock.
If you want to think of some thing scary think of what would happen with external hammers if you blow a primer, shooting glasses might help a bit. This is where a well designed floating pin comes totally into its own. If done right when a primer is blown the pin will be blown to the rear sealing off the firing pin hole from escaping gas much as a valve in a car engine when it closes. If you look at many double external hammer shot guns you will find the pins are not set up this way and in many cheep guns retained by only a small screw. Blow a primer here and you could end up with a firing pin bouncing around in your head,OUCH!!!