Rated 5 out of 5 stars

FireFinder 1.04 does not work with Firebug 1.8.0 on Firefox 5.
At least this was the case on both my Laptops (OSX and Win7)
I downgraded Firebug to 1.7.3 and it worked again.

This review is for a previous version of the add-on (1.04). 

Yes, from Firebug 1.8 and later, they changed some of their inner workings. I've found the issues and fixed the problems now. A new version should be available here shortly.