How do I load external JavaScript before local JavaScript?
You can below preprocess function with scope and weight. You would need to set scope as footer and add the variable to html.tpl.php before body tag.

function paddle_theme_preprocess_html(&amp;$variables) {
  drupal_add_js(drupal_get_path('theme', 'paddle_theme') .  '/scripts/footer.sticky.js',
  array(
    'type' =&gt; 'file',
    'scope' =&gt; 'header',
    'group' =&gt; JS_THEME,
    'every_page' =&gt; TRUE,
    'preprocess' =&gt; FALSE,
  ));
}


Also for Drupal 6, you can check the following reference with Advance JS aggregation or LABjs which can do the parallel loading.

http://www.drupalden.co.uk/move-render-blocking-javascript-bottom-page