This is the test case to check if it's possible for other applications (system-config-printer in this case) to modify the firewall.
How to test
First get and install testing packages system-config-printer-1.3.9-2.firewalld.fc17
2. Run system-config-printer
Click the blue 'plus' button. After entering your password you should see a dialog asking you if you want to adjust firewall. Whether you see the dialog and what items the dialog contains depends on what zone the interface is in. For example: In 'trusted' zone you won't see the dialog at all because all trafic is trusted. In 'work' zone it will ask you for allowing of 'mDNS traffic'. In 'public' (the default) it will ask you also for allowing of 'IPP Browse packets'. Press 'Adjust Firewall'.
After this the needed services should be allowed for 60 seconds, see
and check that you see ipp-client, mdns and ipp services.
In the output of system-config-printer --debug you should see something similar to:
Using FirewallD, active zone: public Examining firewall Asking for permission to adjust firewall: The firewall may need adjusting in order to detect network printers. Adjust the firewall now? - Allow all incoming IPP Browse packets - Allow all incoming mDNS traffic Fetching devices after firewall dialog response