This is a fresh install using the image OPNsense-17.1.4-OpenSSL-serial-i386.img.bz2. When I go to the Firmware page All three (Updates, Plugins, and Packages) show nothing.  
			
			
			
				Looks like a bug.  Might be browser specific. 
{"status":401,"message":"Authentication Failed"}
I switched to using HTTPS and the problem went away.