User experience stability is often a real problem in the corporate or institutional world. Keeping a maximally stable version of Firefox will help corporate users a lot - it's not even necessarily about stability as much as it's about user retraining, in-house extensions, etc.
For most companies what version of firefox probably doesn't matter. However, there are tons of legacy desktop apps in government, call centers etc where installing a new version of firefox will break the application. Hell, the callcenter my company uses an app that will only work with certain versions of ie. The company that made the app went out of business years ago and the only thing the call center has is a binary they install on all desktops.