Answered question
Is it possible to use an external firewall (pfsense, or any other router) instead of the built in one?
Yes, after you you bought the good router, login to Fizz modem and disable "residential gateway", this make modem bridge mode.
link: 192.168.0.1 , username is cusadmin , password is your wifi password.
Other answers
Yes you can use brdige mode by Disable the residential gateway feature
Normaly you should be able to disable the wifi plug your equipements in the modem and use yours instaded of Fizz one's.
You Should make Rose H. best answer!
(Thanks Rose)
Yes you can ! I do!
As mentioned by Rose, just go throught your router and modify settings.
Alexander,
Are you inquiring regarding an external router with it's built-in firewall, or a firewall program? Let's talk, I think this is a good question and it deserves our attention.
Respectfully,
George