Netmon от Konrad Papala

Network monitor - view the HTTP headers of the current page, or globally, from all tabs. You can use it at any time, also *after* the page has loaded.

This is useful when there are random errors in some cases and you just want to see what happened, list the past requests.

It also constantly displays current count of requests in any given tab.

It's open source

If you have any suggestions, please don't hesitate to reach me on konradpapala@gmail.com or file an issue on the github page above.