The Firefox memory issues may have little to do with Firefox itself, at least in some cases. I found the culprit was actually the popular Zone Alarm firewall on my PC. There is some sort of coexistence problem with Zone Alarm and p2p or tunneling applications that cause its memory usage to continually grow. For some reason, this growing memory usage also happens to Firefox. The solution for me was to remove Zone Alarm and repalce it with the free Comodo Firewall Pro. My memory issues with Firefox and the firewall are gone.