Examine source code of Expand URL

{
  "name": "Expand URL",
  "description": "Expand any URL to see where a shortened URL is going to take you. Perfect to check if the final link destination is safe.",
  "version": "1.3",
  "manifest_version": 2,
  "permissions": [
    "contextMenus",
    "<all_urls>"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": {
      "16": "/assets/images/icon-16.png",
      "32": "/assets/images/icon-32.png",
      "48": "/assets/images/icon-48.png",
      "128": "/assets/images/icon-128.png"
    }
  },
  "icons": {
    "16": "/assets/images/icon-16.png",
    "32": "/assets/images/icon-32.png",
    "48": "/assets/images/icon-48.png",
    "128": "/assets/images/icon-128.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{df0f10c4-331e-4449-803e-577ceefbdaf8}"
    }
  }
}