Global Filter as main menu drop down link
To rewrite your taxonomy URLs (you should probably rewrite your question to this end) you can use the following.

/*
 * Modify taxonomy uris to point back to facetted search
 */
function my_module_entity_info_alter(&amp;$entity_info) {
  $entity_info['taxonomy_term']['uri callback'] = '_my_module_term_uri';
}

/**
 * Rewrite term URIs to point to our search query.
 */
function _my_module_term_uri($term) {
  $path = null;
  // Do your stuff to get your path correct.

  // Return your path if you've managed to rewrite it.
  if ( $path ) {
    return array(
      'path' =&gt; $path,
      'options' =&gt; array(), // url style options
    );
  }

  // Otherwise just return the default.
  return taxonomy_term_uri($term);
}