There are many ways to face the Berlin Defense, probably the most reliable variation for Black, along with the Petroff. It's possible to choose a long-term strategic game with 4.d3 to fight in the endgame like how Kasparov got so much headache in his match with Kramnik or look for a computer line in which your opponent needs to remember many moves to make a draw. Firouzja chooses the last option.
1. e2e4  1... e7e5  2. g1f3  2... b8c6  3. f1b5 