Get element from parent doc

Hello everyone,

I am working now with the mozilla firefox-0.9.3-source (C++) enviroment and 
i would like to go over all the buttons in some XUL file in order to find 
the nearest button to the selected one.
I would like to know how to get from the document the buttons list from all 
frames and from each button its position.

My starting point is the nsEventStateManager.cpp in PostHandleEvent method.
I want to take the main document and to walk on all frames and in each frame 
all elemetnts.

how do I get the frame holder and get the element list?

Thanks.
Nir.