It is possible to activate the "Router" mode (NAT) of the Freebox.
Pros and Cons
The freebox will then act as a firewall and protect your computer against external itntrusion. It makes it easier to share the internet connection (if you have a hub or a switch on the Freebox V5).
The Address Translation (NAT) feature of the router mode can be problematic for some software that are used as server (gaming, P2P, etc..), But it can be configured. Note that: It is highly recommend to activate the router mode: This greatly improves the protection of the computer (in case of failure of personal firewalls such as ZoneAlarm).