This typical exchange sac gives Black overwhelming compensation.
1. e2e4  1... c7c5  2. g1f3  2... b8c6  3. d2d4  3... c5d4  4. f3d4  4... g8f6  5. b1c3  5... e7e5  6. d4b5  6... d7d6  7. c3d5 Since it was used in some games of the Carlsen-Caruana match, this move has become as important to opening theory as the old main line with 7.Bg5. 7... f6d5  8. e4d5 This is considered better than the alternative 8...Ne7. 8... c6b8  9. d1f3 A tactical and risky line. White wants to get the queen to c3 or a3, and the game becomes very direct, where the price of forgetting the analysis is very high. More on this shortly. 9... a7a6 It's a good idea to attack the knight immediately. 10. f3a3 The point of White's previous move. The knight is indirectly protected, thanks to the pin. Of course, Black always has the option of capturing the knight anyway and then playing to exploit his development advantage with the out-of-play white queen in the corner of the board. 10... f8e7 Time to finish development. 11. c1d2 Firouzja probably got his analysis mixed up. 11... e8g8  12. d2b4 This makes things even worse.