Reset IE - http://support.microsoft.com/kb/923737

Try Facebook login again.

 

thank you for the help.. it's fixed now..

 

oh, seems like my facebook is ok in google chrome but it still isn't in my mozilla firefox

 

Back your Bookmarks up in Firefox first:

Bookmarks>Organise Bookmarks>Import and Backup>and hit the drop down menu and select 'Backup'. Back them up to your desktop for easy finding. (the file will be a .json file and have the date in the name like : bookmarks-2011-03-22.json

Now uninstall Firefox via the Control Panel (add/remove programs). Then reboot the computer. Re-download Firefox and then re-import your bookmarks again (same way as you backed them up, but instead of selecting 'Backup' choose 'Restore' and point to where ever you placed then (desktop etc)