FOLLOW UP:  It appears the latest Firefox update 3.5.7 may have resolved this issue.

Problem:  This is a very interesting problem that I had and it only existed in Firefox 3.  I use list to organize friends from work, home town, etc.  I recently added a friend to one of the list.   When I went back to All Friends and selected the friend list that I added them to, they did not show up.

  While checking the problem I was curious is IE 8 and Google Chome had the same problem and they did NOT.  So now I had it isolated to a FireFox problem.  I spent about an hour trying to figure out why it was not displaying.  I out of curiousity figured it might be a caching problem so I tried deleting offline files and reducing the size to 1 MB.  This made no difference and the problem still existed.  

  Out of frustration I uninstalled firefox and reinstalled it, which to my surprise the re-installing Firefox did NOT fix the problem. 

  I will post a resolution if I find it, but I just wanted to get this out there so you would know your are not crazy in case you have the same problem.

FOLLOW UP:  This is very interesting.  I didn't find a fix for firefox, but I did determine it is definetly a Firefox unique problem.  IE 8 and Google Chrome to NOT have this problem.  I have or at least tried submitting a trouble ticket to Firefox, but it was a pain.  Seems they don't take problem reports very easily. 

Anyway if you have this problem, use another browser to edit your lists.