New to Zimbra, Admin Panel stopped working in FF

[billiton]

Hello all,

I just set up my first Zimbra server and it looked quite well until suddenly yesterday the admin panel stopped working in Firefox! It shows flawlessly in IE and Chrome, but in Firefox all I get after logging in is a small logo in the upper left corner and a bigger one in the center of the window.

Where is the place to look for the cause of this?