David, you might find this bug report interesting.
Does this still leak in firefox 3 beta 2?
This bug was reported on Firefox 2.x or older, which is no longer supported and will not be receiving any more updates. I strongly suggest that you update to Firefox 3.6.3 or later, update your plugins (flash, adobe, etc.), and retest in a new profile. If you still see the issue with the updated Firefox, please post here. Otherwise, please close as RESOLVED > WORKSFORME http://www.mozilla.com http://support.mozilla.com/kb/Managing+profiles http://support.mozilla.com/kb/Safe+mode
No reply, INCOMPLETE. Please retest with Firefox 3.6.x or later and a new profile (http://support.mozilla.com/kb/Managing+profiles). If you continue to see this issue with the newest firefox and a new profile, then please comment on this bug.