@ XIIIX,
I have tested your site on 3 different computers, one xp, one vista, and one win7 with IE and firefox on all of them.
You site seems to be working correctly on all of them. One thing you may be seeing is if you are logged in already with a 4images account and then press the facebook ligin button. It may be logging out the current user (because the e-mail is different) and then logging back on with the facebook user which makes 2 window refreshes.
@ daniel.carneiro,
I see the problem, You have added 2 new tables with those names. You need to add those 2 fields to your 4images_users table.
In phpadmin open up your 4images database, then open up the 4images_users table, then in the sql tab run this command to add those two fields and you should be good.
ALTER TABLE 4images_users ADD (`fb_userid` varchar(255) NOT NULL,`fl_facebook` enum('new','normal','registered') NOT NULL DEFAULT 'registered')
Make a backup first just in case...