Examine source code of My IP:

{
  "name": "My IP:",
  "description": "Show My IP address",
  "version": "0.1",
  "homepage_url": "https://github.com/Eddie-Burbank",
  "manifest_version": 2,
  "author": "(Original Author TwiN) Edited by Edward Burbank",
  "icons": {
    "16": "data/icon-16.png",
    "32": "data/icon-32.png",
    "64": "data/icon-64.png",
    "128": "data/icon-128.png"
  },
  "browser_action": {
    "default_title": "Display your IP address",
    "default_popup": "data/index.html",
    "default_icon": {
      "16": "data/icon-16.png",
      "32": "data/icon-32.png",
      "64": "data/icon-64.png",
      "128": "data/icon-128.png"
    }
  },
  "permissions": [
    "webRequest",
    "https://api.ipify.org/"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{a8cc2357-101a-4361-9be2-84eac4e83467}"
    }
  }
}