How to see final html when http requesting

Question

I call a http request to get the html of a url. The same also happens, for example, when doing "view source" in Firefox. As you know, the html is different than the final html of the site as it is seen in the browser itself.

Is there a way to call the http request of a url and "do something" so I will have the final "version" of the html including everything that is there when the site ends to load?

The Firefox was an example, I meant calling a http request with a http client, using Java for example. I call a http request to get the html but the html is the "before" state.

Thanks