Hello. If you can ping the gateway and not Google's DNS server probably you're not forwarding traffic to the internet.. Everything should be ok with the pfsense box because you can ping the gateway that is beyond the wan interface...
My gess is that you have some type of proxy in place somewhere... Maybe you have the proxy configured on the computer, and for that reason, the computer can forward trafic to the internet..
The problem is that you dont have configured any type of proxy on the pfsense wan interface
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