Linux xbmcbuntu 11 + Zotac nd22 + xwindows

Team,
my xbmc box is up and running, still in the process of tuning.
1. CEC super-8 wokring -> Pana plasma
2. HDMI + Audio working.
3. Logitech "UNify" kb+mouse working
3. Installed firefox, running however there are screen sizing problems
When I run firefox though the 'Launcher" it start up an xwindow.
However, the resolution does not look right.

How do I configure the system so that it will run 1920x1080 @ 60hz when I launch apps ?
How do I get the system to always use 60Hz as it appears to change to 50hz when I try to launch any apps ?

cheers,
dg