I've spent the last few weeks trying to integrate sametime dojo widgets into a portal theme and I used firebug extensively to debug my code. Dojo is difficult to debug because of the way it injects code using the requires function, everything shows up as an eval.
I didn't know this, but there are quite a few firebug extensions out there, though none really for dojo. IBM has developed a dojo extension for use in their rational developer products, but since I use eclipse I was out of luck. Thankfully IBM has a history of participating in the open source community and appears to have contributed their code to the firebug community.
The code can be found at http://code.google.com/p/fbug/source/browse/#svn%2Fextensions%2Fdojofirebugextension
I downloaded from their SVN server and executed the build.xml, drag/dropped the resulting dojofirebugextension-1.0a6.xpi into firefox and now I have a nice dojo interface for firebug.
Thanks to Patricio Reyna Almandos and Fernando Gomez (IBM Argentina) for putting this together.