Fixed, there was a problem with my template where I converted it from joomla 1.0 to 1.5. However there was some code that was never converted and as a result cause this problem.
The issue is fixed now, thanks for the assistance.
Please note that I have the same issue. I have checked the mootools inclusion and it is working fine. When I click on the Login with Facebook, nothing is showing. It will be helpful if someone can tell me what has to be done.