FF cannot run on both local desktop and remote virtual desktop concurrently.
In a corporate environment, using roaming profiles/AD/etc. using Windows 7, 10 clients and remote desktop connection to virtual desktop on a Server 2012. Problem can be replicated in Windows 7 thru 10, using FF 52ESR through FF58. User with local desktop starts FF. Opens web link to Remote desktop, which is a full virtual desktop hosted on a Server 2012 FF cannot be opened on Virtual desktop, says FF is already running. Close FF on local desktop, FF can now run on Virtual Desktop. If FF still running on virtual, cannot reopen FF until it closed in the virtual environment.
This error had me stumped for days. I still cannot wrap my head around why this is even possible!!! The fact that it is possible is wrong on so many levels.
Domain/AD/profiles etc. are all configured as one would normally expect in a Windows Corp. environment.