Born in Harrison, New Jersey, Firth received an Artium Baccalaureus degree from Indiana University in 1940 and was in the United States Navy as a Lieutenant during World War II, from 1941 to 1945.
He received a Bachelor of Laws from Harvard Law School in 1948, remaining a United States Naval Reserve as a Lieutenant from 1946 to 1952.
He was a judge of the Los Angeles County Superior Court from 1967 to 1974, also serving as a lecturer at the University of La Verne College of Law in La Verne, California from 1971 to 1973.
[1] On February 6, 1974, Firth was nominated by President Richard Nixon to a seat on the United States District Court for the Central District of California was vacated by Judge Charles Hardy Carr.
He assumed senior status due to a certified disability on October 31, 1979, and served in that capacity until his death on January 4, 1984.