Add

$config['listing_uri'] = 'listing';

to cms_config.php

If you want something else like ‘property’->’firma’, then you need additional:

In ‘application\config\routes.php’

After:

$route['listing/(:num)/(:any)/(:any)'] = "property/$1/$2/$3";
$route['listing/(:num)/(:any)'] = "property/$1/$2";

Add also:

$route['firma/(:num)/(:any)/(:any)'] = "property/$1/$2/$3";
$route['firma/(:num)/(:any)'] = "property/$1/$2";