His interest in physics and astrophysics began while serving in the army, during which time he was assigned to the Los Alamos National Laboratory.
He moved from cosmic rays to radio astronomy (particularly of the Sun) when he began work at the Carnegie Institution of Washington's Department of Terrestrial Magnetism.
[3] Firor left the Carnegie Institution of Washington in 1961 to become director of the High Altitude Observatory (HAO), a position he occupied until 1968.
Later in his career, Firor took a keen interest in the intersection of science and society, and he became one of the earliest and most eloquent spokespeople on the dangers of human-induced climate change, testifying before Congressional committees and addressing a broad variety of audiences.
Firor and his second wife, Judith Jacobsen, co-authored The Crowded Greenhouse (2002), on the links between climate change and population growth.