Hi!
So for the code to work you need to navigate to a http site, this initial firefox page will not work nor be injected. When I said to check source code I meant with the page you are using to inject the code. In this initial page it’s common to don’t get responses as you are not requesting any page at the moment, the requests you see in terminal are just default packets sent by the browser when you open it.

And you didn’t answer my question? Is the browser working? I mean is it loading the pages normally?

Let me know.
Diego