Hi friends, watching the log of the site I saw that most of the Firefox users are experiencing problems with autologin and as a conseguence with the infamous cookies.
There is a radical solution for it and I found that is the only thing that really solves the problem.
First close all Firefox windows.
I've the italian version of windows XP, however you've to delete a file called cookies.txt , this file is located under a directory in this path:
c:/Document and settings/(your profile name)/application data/Mozilla/FireFox/Profiles/(strangecharacter).default/
Some of these directories are hidden or system directories so in order to see them you've to change the overall settings for directories using the "Tools" link in the main bar over a directory.
Once done Firefox will recreate the file himself and will write the cookie in the right way. Be warned that deleting that file you'll have to login again on each site you'll go (for the first time).
I hope this is useful for you...