TCP Fast Open (TFO) Support
Does pfSense support TCP Fast Open? Basically it is a performance optimization to TCP to save a round trip (initial 3 way hand shake).
More info here: https://tools.ietf.org/html/rfc7413
I would be using it for a case where I setup a port forward, traffic going to pfSense and then pfSense sending the traffic node behind pfSense. So both incoming and outgoing connections are at play.
In a port forward the TCP session is not terminated in pfSense so it would not have to support it explicitly. The only issue I could see there would be pf rejecting the TCP state if the packets are flagged incorrectly. However it doesn't appear that they are so I imagine it might just work with no changes. If it does see that traffic as out of state for TCP you can add firewall rules to pass it anyway. As shown here but obviously a different cause: