Examine source code of Easy IP Display

{
  "manifest_version": 2,
  "name": "IP Display",
  "version": "1.1",
  "description": "Displays your IP address",
  "permissions": [
    "activeTab",
    "http://*/*",
    "https://*/*"
  ],
  "browser_action": {
    "default_popup": "popup/popup.html",
    "default_icon": {
      "48": "logo.png"
    }
  },
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": false
  },
  "icons": {
    "48": "logo.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{54e29d71-fccd-4e74-8bbb-a9efcd5ab350}"
    }
  }
}