There is a chance that the web site has some kind of a coding quirk which stopped it working under Firefox. Maybe the site designers have only tested it with Chrome and Edge. If so, though, you'd think their tech guy would know that (unless it was a recent regression that the support team is not yet aware of).

I think it more likely that you've got a firefox plugin that's interfering. In Chrome, I use both AdBlock Plus and UBlock Origin, and on rare occasions I have to disable one or both of those plugins for certain web sites to work. Things like login screens are often where that sort of issue is most noticeable.