Firefox firebug is showing an error similar to the following:
SyntaxError: syntax error <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//E
It's actually because onr of your script references cannot be found and is getting a 404.
Check for a typo in your src path, a mistake in your relative path folder location, or an external reference not existing anymore.
<script src="something wrong here"></script>