Hi,
just patched to 0.9.9.9 on a dev site, and now the widgets.php admin doesn’t load… the footer scripts are being output in an infinite loop. Kill the page load and the js never activates the editor, so widget editing is broken. Commenting out the single line below, from lines 292-309 of includes/class-piklist-form.php allows the page to load properly.

       if (in_array($pagenow, array('widgets.php', 'customize.php')))
    {
      if (!class_exists('_WP_Editors'))
      {
        require(ABSPATH . WPINC . '/class-wp-editor.php');
      }

      if ($pagenow == 'widgets.php')
      {
        add_action('admin_print_footer_scripts', array('_WP_Editors', 'editor_js'), 50);
  //     add_action('admin_footer', array('piklist_form', 'editor_proxy'));
      }
      else
      {
        add_action('customize_controls_print_footer_scripts', array('_WP_Editors', 'editor_js'), 50);
        add_action('customize_controls_print_footer_scripts', array('piklist_form', 'editor_proxy'));
      }
    }

Any ideas?
cheers,
Hugh