Mac’s are not often used for Openfire. If you are using an external database or LDAP wihch are not on the same server then you need only openfire/conf/openfire.xml. If you are using the embedded database you need also the openfire/embedded-db/ directory and its contents.
Anyhow the whole openfire directory should contain only a few MB, so you should be able to make a backup of it.
I think that you need also the old installer if you want to restore the same version as the installer adds the rc start and stop scripts.