User Management System approach for Group and Firm

Question

I am creating a User Management System and need your advice.

3 entities:

1. Users
2. Firm
3. Group

Each user will belong to one Firm. Some users (not all) may belong to Group. Group is a combination of Firms. (E.g. 3 firms in a group)

The data will be displayed according to user's firm or group, if a user belongs to firm (but not group), then firm level data will be displayed. And if the user belong to group then group level data (e.g. 3 firms' data) will be displayed.

Is my below mentioned approach correct for this purpose:

CREATE TABLE `user_account` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `firm` varchar(45) DEFAULT NULL, # each user belong to a client firm
  `group` varchar(45) DEFAULT NULL, # some users may belong to client group
  `name` varchar(45) DEFAULT NULL, 
  `username` varchar(15) NOT NULL, # USER ID
  `password` varchar(255) NOT NULL,
  `email` varchar(40) NOT NULL,
  `account_creation_date` datetime DEFAULT NULL,
  `active` tinyint(1) DEFAULT '1',
  `token_code` varchar(255) DEFAULT NULL, # for password recovery
  `token_creation_date` datetime DEFAULT NULL, # for password recovery
  PRIMARY KEY (`id`),
  UNIQUE KEY `username_UNIQUE` (`username`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

CREATE TABLE `permission` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `user_id` int(11) DEFAULT NULL, # FOREIGN KEY user_account.user_name
  `association` varchar(45) DEFAULT NULL, # Firm or Group
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;