Getting the login screen presented locally on the server is normal behavior of Windows Servers. (The server is already fully booted if this is presented, or loads some components not started yet up in background.
Firefly is no core component of WHS, ony an Add-On. Disable the service in the Services console, if you don't need the functionality of that media server.
After logging in to the server, open a command prompt and enter the command
ipconfig /all
Post the output here. Does the server have a working Internet connection? Can it ping the default gateway, and can the server be pinged from a client by name/by IP address?
Eventually the Windows Firewall has been reset to default settings, eliminating the connectivity for WHS related components. Check, if the WHS firewall still matches the settings listed
here.
Best greetings from Germany
Olaf