your typical off the shelf router is a firewall as well, it just has limited features in allowing configuration of the rules. Many of them have very limited outbound controls, and inbound are all pretty much just port forwards with varying degrees of features depending on the make and model.
But in a nutshell out of the box pfsense is same as any off the shelf home router in what it does. It nats, all inbound traffic that is not direct answer to a request is blocked, while the default outbound rules from lan are any any. This is pretty much what every off the shelf router does.
Where pfsense allows you to go way beyond what any off the shelf router would allow you to do when you want to get fancier than that. But if you want to use it like that - that is pretty much how it is out of the box.
And yes you could even enable UPnP if you want it.. Where your off the self router is normally just an on and off checkbox, pfsense allows you to get fancier with allows and deny specific ports or deny from all except a specific IP to request, etc..