I guess that Zimbra is detecting "Android" in the UA instead of "Mobile" and therefore it's not recognizing Firefox OS as a mobile platform, i.e. not preselecting "Mobile" in the "Version" dropdown. When selecting that one for login, it works pretty well there, though. This can be seen by going to https://mail.mozilla.com/zimbra/ in the browser of a Firefox OS device.
Confirmed. Firefox for Android is working. Firefox OS is getting the desktop environment.
I filed this one a while back. https://bugzilla.zimbra.com/show_bug.cgi?id=80575
Mike - AFAIK Zimbra's source code is open. Care to submit a patch?
Happy to give it a stab.
Fixed over at https://bugzilla.zimbra.com/show_bug.cgi?id=80575.