Funny, and true at least in the company I'm working for (officially supported browsers are primarily IE11 and optionally Chrome).
A colleague told me a few months ago that Firefox was not supported because it did not support some Windows "policies" (Windows or Active Directory? Not sure, no clue about that stuff) but that Firefox was going to support them soon... .
Both the ADMX templates for Windows and preference .plist for macOS are available from GitHub [3]. The full list of configurable preferences can be found on SearchFox.org [4].
As of Firefox 67 there are quite a lot of settings that can be managed now. Certainly enough for Firefox to be deployed in enterprise environments.
There was also a really interesting talk at MacADUK 2019 by Mike Kapley on the work Mozilla has done so far to support enterprise deployment [5].
[1] https://bugzilla.mozilla.org/show_bug.cgi?id=1433136
[2] https://github.com/mozilla/policy-templates/blob/master/mac/...
[3] https://github.com/mozilla/policy-templates
[4] https://searchfox.org/mozilla-central/source/browser/compone...
I use Firefox for all my browsing needs except for Google apps, for which I keep an install of Vivaldi around. I only really fire up Chrome if some stupid internal workplace app refuses to work on anything else. It truly is the new IE.