It's probably just an IT thing. Many companies opted to deploy Firefox internally as an alternative to IE because it played well with their software management tools (as opposed to Chrome, which only got centralized version management later). In IT/helpdesk settings, you want to know what specific browser version your users are running to ensure intranet apps are compatible.

Because, you know, legacy. Anyone who's used Siebel, Oracle intranet apps, etc. knows what it's like.