That's weird. I used to work in a very secure facility (think actual air-gapped supercomputers where network access is building-LAN only) and Firefox was the only approved browser.
(you still need to get data in and out sometimes, Chips can be misused as radio antennas, loudspeakers can be used as microphone and do ultra sonic data transmission to other devices etc, so still making sure the software is under control on the Air gapped computer sounds like a good idea)