How can I prevent Stateful Firewall installation on MacBook Air?

We can't see your machine, much less read your mind. We rely on you to give us enough information so that we can understand your issue if we are to help. We need a full description of the issue, information on what devices or machines you're referring to, the operating system (and version of it) currently on the machine. What you expect to happen, and where it fails. Err on giving too much information rather than too little.

I will take a stab at this

StatefulFirewall is a potentially unwanted program that injects advertisements into websites you visit and changes your browser’s default search engine and homepage.

StatefulFirewall is commonly bundled with other programs that you download from the Internet.

https://malwaretips.com/blogs/remove-statefulfirewall/