It's client-server (Firefox <=> management console). There's no other app needed client side, it's all built into the browser.
what about WAN users? intermittent connections?
Supported (one of our core developers often works on a spotty 5G, so we got rather loud feedback when this broke...)
multiple profiles? per-user or per-device? multiple users per device and multiple devices per user? group management? integration with other directory services - or do they reinvent the wheel and I need to input every update in multiple applications? multiple platforms?
Yes to pretty much all of these - minus reinventing the wheel - I think only "multiple profiles for the same user-id" are currently not supported. You'd essentially need to give an alternate login to the users that need this (because that's what triggers the profile selection). I don't think there's technically anything stopping this, just didn't seem like a common enough use case to get in the very first release.
mobile apps?
Not in this first release. (^_~)
Does it reliably autodeploy or do I need to manually do something for each of my 10,000 users?
We expect most will autodeploy over an existing MDM solution (Intune, Fleet, ...).
Again, how much will Mozilla invest in this small group of users, the IT admins?
I'd say Firefox Enterprise's customers are the IT admins, no? The users aren't generally the asking party to get a managed browser.
All I would say is, put something on your website that persuades admins that it won't be a headache, that it will make their workday easier, not harder - regardless of benefits to overall IT goals. Maybe a 1-2-3 screen clips/animations (fantasizing a bit of the content for this example):
1 - Deploy: Add this pref to the FFE application deployment package and FFE management is deployed in every installation!
2 - Open the management console - there's the new installation, and it's automatically listed under the user/device synced from directory services!
3 - Manage: (shows user/device in a group, and a nice set of clearly defined - non-ambiguous - hierarchical checkboxes for that group's prefs).
And actually make it reliably that easy - which I know means more work on your end and isn't always practical, but it makes an enormous difference IME. Get people talking about how easy it is. Solve their busyness problem.