Network comprehension question: localhost vs. local IP address

[Volker Wysk]

Hi!

The Moinmoin wiki server can be run without configuration, so you can try it, 
without the hasszle of configuring everything for Apache. It starts a server at 
localhost:8080. This works.

Now I want to try if it works well with my smartphone. I try the address 
http://192.168.178.20:8080/. Here "192.168.178.20" is the IP address of my 
desktop machine, which is being assigned by my Fritzbox router.

I get the following error message from Firefox: "Fehler: Verbindung 
fehlgeschlagen; Firefox kann keine Verbindung zu dem Server unter 
192.168.178.20:8080 aufbauen." Translated back to English: "Error. Connection 
failed. Firefox can't establish a connection to the server running under 
192.168.178.20:8080".

This occurs even when I try to access the 192.168.178.20:8080 address from the 
desktop itself, no other device involved. I, however, can connect to http://
192.168.178.20/.

Now I'm puzzled. What is the difference between localhost and 192.168.178.20? 
Why does it connect to the default HTTP port, but not to 8080?

Bye
Volker