If it came in MSI format for easy installation to Windows workstations, and could be managed by GPO and Apple Open Directory then it would be perfect. It would also need to work well with things like Sharepoint, but I suspect that's an issue for the people designing sites in Sharepoint rather than Mozilla.
I know there's currently a fork of firefox that is designed to work with GPOs, but I'm talking about having it work with the "standard" product out of the box, and being able to control and lock down and any all preferences.
As neobyte says, patch management is also an issue. Firefox's current method doesn't scale for business imho.
Extension management - this needs to be controllable by the enterprise too, there needs to be a way to roll out and "lock" into place a standard set of extensions, regardless of whether or not you want users to be able to add their own, possibly to nominate a trusted location of your own where you publish "approved" extensions, that kind of thing.
NTLM auth - looks like there's a hack to add this to the browser anyway if you look around the web but this needs to be obviously better exposed.