That says:
Add The Things Network nodes
But, don’t, as those are deprecated:
The support and maintenance for this SDK has been discontinued, it is not recommended to use the SDK for new projects.
Instead, see https://www.thethingsnetwork.org/forum/t/mqtt-in-node-red-howto/39909.
As for firewalls: an MQTT client opens a connection to the remote broker (server) on port 8883 (or 1883 for non-TLS). A client does not need incoming connections.