starting with javaXPCOM

Hi

I'm just starting with javaXPCOM. What I'm trying to do is open an url
and save the document in the filesystem. Unfortunately, I couldn't find
documentation of the calling steps for archiving this. In particular,
I'm confused about the implementation of IAppFileLocProvider in the
javaxpcom initialization:
Mozilla.getInstance().initEmbedding(grePath, grePath, new
LocationProvider());
What are the semantics of the methods of IAppFileLocProvider ? Has
anybody examples?
What are the differences between initEmbedding() and initXPCOM() ?

Well, I really want to embbed javaxpcom but I can't find documentation
about it. For example it would be very nice if somebody publish an
example that open a url.

Well, thanks in advance. Any tips on what shoud I read first will be
appreciated. Excuse me for my bad english. 

Sebastian