Rated 3 out of 5 stars
Didn't work on a latest (1.8b6) FB beta -- throws a lot of errs into errcon and shows nothing in the pane. Anyway looks (but only "looks") useful and handyThis review is for a previous version of the add-on (0.9.6.1.1-signed.1-signed). This user has a previous review of this add-on.
The last version (0.9.7) is compatible with Firebug 1.8 so this should no longer be a problem.
If you find a bug or if you have an enhancement idea, please don't hesitate to create an issue in the issue tracker here: http://code.google.com/p/firepath/issues/list