Does you XULRunner application contain a <browser> and display web
content? Firebug is not really designed to debug the XUL chrome
itself. Firebug is designed for debugging HTML web content.
If your app does display web content and you want to use Firebug in
the app, then you need to do a few things:
1. Add EnableExtensionManager=1 to your application.ini file as
described here: http://developer.mozilla.org/en/docs/XUL_Application_Packaging#The_.5BXRE.5D_section
2. Prefs for ExtensionManager as described here:
http://developer.mozilla.org/en/docs/XULRunner_tips#Extension_Manager
3. You will need to tweak the install.rdf in Firebug similar to the
changes described for Venkman - here: http://developer.mozilla.org/en/docs/XULRunner_tips#Venkman
4. You will also need to tweak the Firebug overlay or make a new
overlay specific to your application, so Firebug can load itself into
your app.
5. Find a way to install Firebug, although since you need to unpack
the XPI anyway you can probably just copy the extension into the
"extensions" folder of your app (for XR 1.9) or in xulrunner ( for XR
1.8.0.x and 1.8.1.x)
As you can see, there are more than a few things to do. I added DOM
Inspector and Venkman extensions to my XUL Explorer xul app. You can
download XUL Explorer and see what I did to get those working:
http://developer.mozilla.org/en/docs/XUL_Explorer