JFBCLogin requires mootools to work, so I'm sort of confused. Is JA Larix using a special or modified version of mootools in some way? The JFBCLogin module makes a Joomla call to use the packaged version of Mootools. If you can explain more, that would help. Also, look in the source on your page to see if multiple mootools.js files are being loaded. Finally, feel free to send your URL and we can look to see if we see something obviously wrong.