Examine source code of Google Cache Retriever

{
  "name": "Google Cache Retriever",
  "description": "The appearance of this Firefox add-on may include an icon or button that is installed on the browser toolbar. When you click that icon, a small window or dialog box may appear, allowing you to take action. In this case, the interface may display a text field for you to enter the URL of the page you want to cache from Google Cache.",
  "version": "51.0",
  "manifest_version": 2,
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_action": {
    "default_icon": {
      "19": "images/icon19.png",
      "38": "images/icon38.png"
    }
  },
  "icons": {
    "16": "images/icon16.png",
    "48": "images/icon48.png",
    "128": "images/icon128.png"
  },
  "permissions": [
    "tabs",
    "activeTab",
    "contextMenus",
    "<all_urls>",
    "http://*/*",
    "https://*/*"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{e48a9a7a-64b3-4a1a-a0e3-3907afaae17f}"
    }
  }
}