A lot has changed since my last XUL related post, several new tools now exist
that can help you learn XUL more effectively while many a good resource like
www.georgenava.com have gone down.
INTRODUCTION TO XUL
XUL TUTORIALS
Mozilla developer center's XUL tutorial
Building applications with XUL and javascript
Create Web applets with Mozilla and XML
XUL: The Future of User-interfaces on the Web
HOWTO: Getting Started with Linux Standalone Apps using XUL
XUL Element preview and reference
XUL REFERENCE
Mozilla developers center-XUL reference
FIREFOX EXTENSION TUTORIALS
Nerdshift-Firefox extensions tutorial
BornGeek-Firefox toolbar tutorial
How to create Firefox extensions
Setting up extension development environment
Firefox Extension Development Tutorial
Captain's Mozilla XUL LOG - read local files and write local files
XUL, XPI and Firefox/Mozilla extensions
XUL BOOKS
Creating Applications with Mozilla
Rapid Application Development with Mozilla
XUL TOOLS
Extension Developer's Extension
eclipseXUL - XUL Support for Eclipse
XULBooster- another eclipse plugin for XUL
GUID Generator (From the evil corporation)
FIREFOX LINKFEST (HUGE COLLECTION OF LINKS RELEATED TO FIREFOX AND XUL PUT TOGETHER BY OTHER GUYS)
XUL BASED APPLICATIONS
Democracy player (there is a XUL port of the democracy player)
REMOTE XUL
Remote XUL applications with PHP
Creating XUL applications with PHP
Creating Rich Web Applications by Connecting XUL with PHP
FIREFOX HACKS
Modifying Firefox's Context Menus
Firefox XUL kiosk browser script (shameless self linking :) )
XUL CHEAT SHEETS
Hope this helps you and sets you on your way to XUL mastery.....