How can a firewall cause printing problems, and how do I troubleshoot it on the HP Photosmart 7520?

Firewalls can block communication between devices on the home network, causing issues such as the printer not being found during software installation, suddenly being unable to print, or the printer appearing as OFFLINE. A quick troubleshooting step is to temporarily disable your firewall to see if the problem goes away, and if your firewall has a 'trusted zone' setting, use it when connected to your home network. You should also allow any HP software that triggers a firewall alert and select any 'remember this action' option so the firewall learns to trust HP software. (Page 5)