Fallen First-Responders' Family Naturalization Fee-Relief Act of 2021 This bill waives certain immigration application or petition fees for an applicant who is (1) an injured firefighter or law enforcement officer, or (2) an immediate relative of an injured or deceased firefighter or law enforcement officer. Specifically, such fees must be waived if the firefighter or law enforcement officer died or was permanently and totally disabled from an injury sustained in the line of duty.