I have a HP printer set up using wifi with CUPS in OM Lx 4.3. It worked when I set it up. And if I remember to turn it on it is still working wifi.
Follow the document @Colin posted. The trick is in getting the correct selection under either “Discovered Network Printers” or “Other Network Printers”. For me “Discovered Network Printers” shows my printer but using that did not work I had to use an entry under “Other Network Printers” and manually enter my wifi printer url. The url of your wifi printer is on the screen of your printer.
As far as the firewall, firewalld, it is set to incoming Allow and outgoing Allow. That is unlikely to be stopping much of anything.