A list of active connection states may be viewed at Diagnostics > States.
This will list all currently active connection states, with their protocol, IP information, and state info.
The IP address information is printed showing the IP addresses involved in a connection and the direction the connection was initiated. If only two IP addresses are shown, it is a state to or from the pfSense box itself. If three are shown, then NAT has been applied.
Each connection through the firewall will have two states: One entering the firewall and one exiting the firewall. Only one of those states will typically involve NAT.
The view can be filtered by typing some text into the Filter expression box and pressing the Filter button. If an IP address or CIDR-masked subnet is entered in to the Filter expression box, then after filtering a Kill button will appear. Clicking the Kill button will remove all states to and from the entered address.
Individual states can be removed by clicking at the end of the row. All states can be reset by using the Reset States tab.