CakePHP shows a different field than id in dropdowns

I have two tables: users and firms:

class Firm extends AppModel {
    var $name = 'Firm';
    var $hasAndBelongsToMany = 'User';
}

and

class User extends  AppModel {
    var $name = 'User';
    var $hasMany ='Post';
    var $hasAndBelongsToMany = 'Firm';
}

I use scaffold var to display all save / view / edit methods, etc. I override the add method as follows:

function add(){
    if (!empty($this->data)) {
        $this->User->create();
        $this->User->save($this->data);
        $this->redirect(array('action'=>'index'), null, true);
    }
    $firms = $this->User->Firm->find('list');
    $this->set('firms', $firms);
}

Everything works fine, but when I use users / add, I have a popup menu with an identifier: "1", "2", etc.
I would like to display the name of the company, not the identifier. How to do it?