You don't have Norton Internet Security running as well do you? I downloaded Firefox and Thunderbird 1.5, at the same time Norton downloaded an update and ever since my Mozilla apps have been going haywire, not seeing my account info or my inbox, resetting themselves to new instals and loosing all my bookmarks etc... It seems that 1.5 is slightly FUBAR as well as NIS. Uninstal NIS and use free ones from the net.