One size doesn't fit all
When I first read this my first thought was that Mozilla were shooting themselves in the foot, but the more I think about it the more I've come to the conclusion that it's not such a bit deal. The key is that one size rarely fits all successfully.
In a corporate environment the key requirements are stability and reliability. You want to know that everything will just work, wizzy new features are all well and good, but since the development / testing cycles take so long it's unlikely any internal apps etc will need the latest and greatest features in the short term. An admin wants control over what users are doing and how they do it, and the certainty that things will work as expected, so they don't end up with those on high yelling at them because something hasn’t behaved as expected. I agree with the comments about "apps should be standards compliant and just work", but in the real world that simply can't be relied upon. Telling the MD that staff can't do their work because the developer didn't follow the correct standards and it's not your fault won't wash.
In a home environment on the other hand most people are more tolerant of stability issues (I know I certainly am), but they want to be able to use the latest and greatest apps etc. Facebook games, streaming videos etc are important at home, not in the work place, so rapid deployment of the latest features is important to them. The raft of add-ons available in Firefox can be great for a home user, but again is a pain for an IT admin.
So, while I wonder if Mozilla are being short sighted in ignoring Enterprise environments, if their aim is to target a specific niche (eg home users) then in that respect this is probably the best way to do it, since MS clearly aren't aiming their efforts in that direction.