Refspoof works well for what it's supposed to do. However, I decided to delete the refspoof add on since I wasn't using it very much. I had it on the disabled referrer option, and uninstalled it. Then, I began having problems on various websites because a referrer issues. I had to reinstall refspoof and set the enabled referrer option to fix these issues. Very irritating!
with 0.9.5 the high cpu usage should be a thing of the past and the other functions got adapted as well for firefox 3 .. download it from the sandbox https://addons.mozilla.org/en-US/firefox/addons/versions/4513 (you need to be logged in) as it didn't yet get pushed through yet