Is it possible for example to create an iframe with www page inside and print all the HTTP requests in kind of text element like label or something (it doesn't metter in which one, I just want to preview the headers.
You need observerService to listen to http-on-modify-request (request headers) and/or http-on-examine-response (response headers).
I don't have complete code at the moment, but see these snippets to get the idea.