Rated 5 out of 5 stars

A version working with the Element Properties add-on (recent Fx versions) is available in the MozillaZine forums:
http://forums.mozillazine.org/viewtopic.php?f=48&t=1674905

Maybe you could adapt this tiny change? :)

This review is for a previous version of the add-on (0.3.2). 

As promissed in my earlier reply, the just released 0.4 cooperates with the Element Properties extension.