I was about to post that RefControl now seems to work on all my systems, but double checked and, alas, no. RefControl is broken on Firefox 3.5 running on Ubuntu 9.04. Time to systematically uninstall RefControl on all my Linux boxes and install Web Developer on each. I can't have a privacy tool that sometimes works on some systems.
Web Developer Add On: https://addons.mozilla.org/en-US/firefox/addon/60
Testing for broken referer blocking: grc.com or http://userpages.umbc.edu/~jmartens/courses/is430/infoleak.shtml