Learning curve - trouble getting onto it !!

Hi
As a newbie I am trying to get on the curve with Mozilla. I keep falling off 
when I cannot identify a method to find out to find out  how something works 
or find a resource which will enable me to find out about it.

Let me illustrate with a specific. 

I have an xul file that works fine. I am about to launch a new window from 
which to load that xul (new process) from a mozilla browser. At the time of 
launch the browser's currently active window displays a loaded web page 
(current page). I want to pass the URL of the current page as an input to the 
new process. My specific question is how can I do that?

My general difficulty seems to stem from a generic failure to understand how 
to find out  the information to enable me to solve such problems. Is there a 
searchable Mozilla cross reference for data sources and methods. 

Comments please
Thanks\

david

-- 
40 yrs navigating and computing in blue waters.
English Owner & Captain of British Registered 60' bluewater Ketch S/V Taurus.
 Currently in San Diego, CA. Sailing this fall bound for Europe via Panama 
Canal.