Writing XUL is a giant pain in the ass and the documentation is lacking any examples.
Here is a good resource
https://forums.mozilla.org/addons/viewtopic.php?f=7&t=384
Excerpt from that page
There is a list of some resources here
https://addons.mozilla.org/en-US/develo … ng-started
This tutorial is quite a helpful introduction
https://developer.mozilla.org/En/Firefo … Extensions
I generally just use MDC (Mozilla Developer Center) for reference (just keep an eye on what version of Firefox/Gecko the documentation applies to)
https://developer.mozilla.org/En
The XUL periodic table is a helpful resource for basic XUL element layout
http://www.hevanet.com/acorbin/xul/top.xul
W3Schools is a useful basic reference for DOM and Javascript
http://www.w3schools.com/jsref/default.asp
There is a list of the Mozilla interfaces here
http://www.oxymoronical.com/experiments/apidocs/
The DOM inspector is a “must have”
https://addons.mozilla.org/en-US/firefox/addon/6622
Anyway that’s just a few that you might find useful
HTH