Issue

It is not possible to include nf_nat_ftp module into firewalld configuration.

According to a manual page man firewall-cmd modules are expected to be included using mentioned syntax:

       --permanent --service=service --add-module=module
           Add a new module to the permanent service.

but including of nf_nat_ftp kernel module for ftp service using mentioned syntax leads to the following error :
Error: INVALID_MODULE: nf_nat_ftp

As the result, netfilter modules couldn't be loaded automatically after complete reload or restart of firewalld service.