This add-on lets you send remote debugging protocol requests to the debugging server, and displays the response.

To use it, just type the JSON message into the textbox and hit Ctrl+Enter. The response is displayed on the right-hand side.

For example, try:

{}

or:

{
  "to": "root",
  "type": "listTabs"
}

To learn more about how this add-on works see the tutorial at: https://developer.mozilla.org/en-US/docs/Tools/Adding_a_panel_to_the_toolbox.