I have not tried it but here are my thoughts:
1. Addons that do not appear at mozilla.org are suspect. Not that all of the addons which do appear at mozilla.org are not
suspect, but at least they appear in a location where users can evaluate and publicly review them.
2. The addon does nothing but increase personal bandwidth use unless the number of people using it reaches critical mass. Hundreds or even thousands of people running this isn't enough to put a fuzzy dent in the data collection database(s).
3. I know that there is a similar addon for Chrome (a browser I don't want to touch) called Chaff. The addon can be found here
and the author can be found on EFNet IRC in his #chaff channel. I don't think this addon has been widely adopted yet either.
4. I think trying to defeat data collection externally is ultimately futile and just puts the public in a constant battle with large corporations and government to see who can one-up the other in the "is it real traffic" race. Similar in concept to the way spammers and email administrators battle back and forth. The removal/destruction of such databases and the permanent future non-collection of further data is more of a solution than a distraction-based workaround... whether that future non-collection comes from honest government (pffft) or real working encryption.