Homelander could not have given a shit less about her. This was about liberty/stormfront. I think at first he liked the idea that he had this weird connection to his father, but I think once it had a moment to settle in and he saw that it seemed like his dad might’ve actually cared about her at some point when he gently looks at her picture, things changed.
How dare liberty think anyone else was perfect like she thought he was perfect? I think he had issue with the idea that she had found anyone else to be this super God that she was constantly telling him he was. She was his, but not in a romantic sense as far as he’s concerned. Something closer to property. And still somehow his father was there first. Firecracker was just a place he could focus his anger. In that moment, I don’t think he was killing firecracker.