Version 1.4.0
In the xfbml javascript embedding mode the function get_footer() is added to loop_start. This puts <div id='fb-root'></div> in the <head> section. Also JavaScript needs to be in the tag <script type='text/javascript'> to be valid.
I ended up changing line 82 from:
add_action('loop_start', array(&$this, 'get_footer'));
to
add_filter( 'wp_footer', array( &$this, 'get_footer' ) );
The <fb:like> is also invalid but this isn't as big a problem.