I am trying to use Putty and VNC Viewer on the client to connect to a Ubuntu host which has X11Forwarding yes and X11DisplayOffset 10 set in the SSHD configuration. I have enabled X11 Forwarding and specified the X Display Location of localhost:10.0 in the Putty client. How does Putty know to use the RealVNC viewer? When I try launching something, say Firefox I get the following which is probably expected since the VNC client is not linked or I do not know what to specify in the VNC client. Do I just need to forward 5900 instead of enabling X11?
$ Error: cannot open display: localhost:10.0 + Exit 1 firefox
Have also tried port forwarding per screen-shot below.