France doesn't have enough nukes to do that. May be, they'll burn down Moscow (if they are lucky/unlucky), but Moscow, however important is expendable. Napoleon had it burnt back in 1812, and then he'd lost the war. And it can piss the Russians off enough to kill 90% of all Frenchies (including women and small children).
Of course no. They want war - they'll have war. The war will came into their cities. It will come with nuclear strikes, it will come with the clouds of deadly poisons, and it will come with genetically modificated germs. In less than one year France will lose more than 90% of their population.
Its pure self-defense. They came in Russia (and Ukraine is part of Russia) - they are dead.