Rated 4 out of 5 stars

Great stuff. Works with FF3 when the install.rdf file is edited to allow later than version "2.0.0.*". Download the latest extension with non-Firefox browser, then:

$ unzip hackbar.xpi install.rdf
$ sed -i -e 's/2.0.0.*/3.*/' install.rdf
# zip -u hackbar.xpi install.rdf

voila! Good to go! (Mac OS X command line or Linux/Solaris command line, only; Windows users are on their own)

This review is for a previous version of the add-on (1.3.2).