using prefs in applications

Is there a document that describes how to use your own prefs in your own 
applications?

fx the use of:
var _elementIDs
in the top of all xul pref document.

also the use of fx prefstring

I'm developing a Mozilla Extension and want the pref stuff to be as easy 
and fast as possible, but I'm not 100% sure how to take advantage of 
some of Mozilla build in pref stuff.


-- 
Henrik Gemal
Mozilla Evangelist

Description of profile files:
http://gemal.dk/mozilla/files.html