You don't have to disable complete Windows Firewall. When you add computers to Notezilla (using Send To->Computers option from a sticky note), Windows firewall will automatically ask you if you want to allow Notezilla to communicate. You would need to add computers on every computer running Notezilla . Note that when adding computers, Windows Firewall should be enabled. Only then it will detect and add Notezilla .
First, make sure at least one computer is added in the computers list in Notezilla . If after enabling Windows Firewall and adding computers, you are unable to send note then you would need to go to the Firewall and configure the PC firewall to allow Notezilla .
You can search for firewall in Windows search box and you will see Allow an app through Windows Firewall . Choose this option and enable Notezilla . If Notezilla is not listed, then click on 'Allow another app' and add Notezilla .
If you are using any other Firewall tool (usually included with Anti-Virus software) then you will have to configure that firewall.
Make sure you do this on all the computers.