I forgot to close this thread. I solved the problem by using
jsd.topLevelHook to trigger my XBL constructor.
It is necessary only for frames/iframes. For top documents,
onLocationChange can be used.
Here is the code, it might be useful to someone else: :-)
http://www.mozdev.org/source/browse/br/multifox/src/modules/main.xbl.js?rev=1.1
--
Jeferson