A floating firing pin is part of the AR15/M16/M4/etc ad nauseum... design.
If you're firing reloaded ammo, make sure your primers are fully seated (below flush with the cartridge head) and that you haven't used small pistol primers in place of small rifle primers. The pistol primers have thinner cups and are supposed to be more sensitive.
You could also avoid greasing or over-oiling the firing pin (and firing pin channel). Too much lube attracts and holds dirt, carbon and other grit. If that happens, your firing pin may get stuck forward, but I really, really doubt that'd happen, given the way the BCG shuttles back and forth.
Excessively dirty chambers can stop the cartridge from fully chambering, letting the gun fire out of battery. Same goes for bent cartridges, dirty cartridges, incompletely sized casings, or bullets seated too long (ought not be a problem if they fit into and feed from the magazine).
Look at the bolt carrier group. Push forward on the firing pin forward and notice it does not protrude beyond the bolt face when the bolt is cammed forward and farthest from the carrier (during unlocking, extracting, ejecting, loading phases of the operating cycle). Now push the bolt back into the carrier (chambering, locking and firing) while pushing on the back of the firing pin and make note of when the firing pin is past flush with the bolt face. That should be near the end of the bolt's travel back into the carrier. That is to say, when the lugs have locked behind the lugs on the barrel extension.
Really, it shouldn't be too big a problem. Use good ammo and keep your gun maintained.
Oh, ya, and have fun.
