browser.devtools.network.onRequestFinished.addListener(listener)
browser.devtools.network.onRequestFinished.removeListener(listener)
browser.devtools.network.onRequestFinished.hasListener(listener)

Events have three functions:

addListener(listener)

Adds a listener to this event.

removeListener(listener)

Stop listening to this event. The listener argument is the listener to remove.

hasListener(listener)

Check whether listener is registered for this event. Returns true if it is listening, false otherwise.

callback

Function that will be called when this event occurs. The function will be passed the following arguments:

request

object. An object representing the request. This object is a single HAR entry object. It also defines an asynchronous getContent() method, which returns a Promise that resolves with an array of two elements. The first element is the HTTP response body as a string, while the second element is the MIME type of the HTTP response also as a string.

Add a listener that logs the server IP address and response body for every network request.

function handleRequestFinished(request) {
  console.log("Server IP: ", request.serverIPAddress);
  request.getContent().then(([content, mimeType]) => {
    console.log("Content: ", content);
    console.log("MIME type: ", mimeType);
  });
}

browser.devtools.network.onRequestFinished.addListener(handleRequestFinished);