Examine source code of GrabMyIP

{
  "manifest_version": 2,
  "name": "GrabMyIP",
  "version": "2.2",
  "description": "Displays the user's public IP, City, Country and ISP in a tooltip when the extension icon is clicked.",
  "icons": {
    "48": "icons/icon48.png",
    "96": "icons/icon96.png"
  },
  "permissions": [
    "*://ipinfo.io/"
  ],
  "browser_action": {
    "default_icon": "icons/icon96.png",
    "default_title": "GrabMyIP"
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{74e1a296-a8c4-4265-8c66-23b90e8a0240}"
    }
  }
}