Government IT worker here: IE was dropped off almost all DoD computers years ago when MS officially ceased support of it. Edge, Firefox, and Chrome come standard with the baseline image at most sites I've supported.

I think this article is also pretty silly. We have scientists, engineers, accountants, logistics, etc. all using various web apps and sites. Rather than fuck around with installing a browser that may or may not be compatible with any of them, we had our image team blanket install Chrome and Firefox to avoid unnecessary tickets. Just because government websites may not require designers to be compatible with Firefox doesn't mean anything for all those federal jobs that don't only use government sites for work.