I don't know about a public site, but you can try it locally by running xul-node-server (see the docs).

server v's client
You may want to take a peak at these comments xul/perl (use.perl.org) for server side (ie: xul-node) or kungfuftrs posts who talks about how to use perl/xul, client side via XPCOM.

what I liked about the discussion on XML-Node was how anything you can do in JS you can do in Perl + XML-Node.

reading mork: perl use for firefox
...but there is not much going on in the above modules. if you want you can read about jwz and mork.pl and how perl saved the day reading the mozilla history.dat file.

update:
yeah sorry for the confusion. rightly or wrongly its pretty much the way I reply as I never get a top level reply option so I comment on the child node.

I've read about mork. I even know the person who helped him reverse engineer this insane format. And this has absolutely nothing to do with XUL. :)


Update: ah, you wanted to make a top-level comment and accidentally replied to something I said. Was it as confusing for you as it was for me? :)