You can put any options in that config file that are listed in the ssh_config man page. So now all you need to do is
ssh mysocksand it will set up a listener on local port 9988, traffic forwarded over ssh to mysocksbox.domain.name. You can then use the firefox switchproxy add on or foxyproxy to point to localhost 9988 SOCKS5. You also want to set network.proxy.socks_remote_dns to true in about:config to get DNS to go through the proxy too. Simple!