Adding a clearfix class to hook_node_view
You can do this in a hook_preprocess_node() function in your theme's template.php file:

function MYTHEME_preprocess_node(&amp;$vars) {
  if (isset($vars['content']['links'])) {
    $vars['content']['links']['#attributes']['class'][] = 'clearfix';
  }
}


Remember to clear Drupal's caches once you've added the function so the system picks it up.