Keyboard navigation between controls

Hi

I  am trying to write a DVD navigation style in fire fox

I want the user to be able to move from controls using the arrows - up down 
left right

I looked at nsEventStateManager.cpp to see what I need to change

Currently the mozilla support only tab order moving between controls and I 
want to give power to move left right too, according to XY location (like 
when you doing so in your TV settings screen)


And ideas - help?
Where I need to start from?

Thanks

Adys