SVG - DOM function calls not working in FireFox 1.5b2

Hello,

I'd like to access the "uncles" elements of a give element in an svg file 
using DOM tree with javascript; the 2 following calls don't work, in both 
cases "element" is a "svg:group" node.

var uncles = ((element.getParentNode()).getParentNode()).getChildNodes();

var uncles = element.getParentNode.getParentNode.getElementsByTagName('g');

Cay you help me fixing this, or give me some hint on where I can get debug 
information in FireFox?
thanks!
Berteh.