If you can't drop the water precisely nor reload in flight at the nearby lake your fire will stay the size of France. BTW that was almost funny, good try.
It actually drops fire retardent/chemicals infront of the path of a fire. When fighting a fire the size of France, it is much easier (and a lot safer) to utilise an army of resources to contain it and let it burn itself out rather than utterly defeat it.
It's size and range and payload enable it to fly very long distances into rural areas and drop precisely a very long long line of retardent, essentialy creating instantly a seamless defencive line stretching nearly a mile in otherwise inaccessable terrain.
There are other aircraft that I think are more impressive, think medium sized (well, large for a sea plane) and capable of skimming a large body of water to rapidly refill tons of water, then flying to drop it and imediatley repeating the process. If weather and conditions are right, they can have a serious impact. That is their downside though to something like the DC-10 though, they cost more for maintenance and need good weather and conditions to rapidly refuel off water surfaces.
