This logstash file currently only handles the firewall logs, and does not conform to the ECS.
To configure pfsense:
Go to the Syslog configuration page: Status -> System Logs -> Settings -> Remote Logging Options
Ensure Enable Remote Logging -> Send log messages to remote syslog server is checked
Ensure one of the Remote log servers is your logstash node.
Enable Remote Syslog Contents -> Firewall Events