Examine source code of Joinchat - WhatsApp Contact Button

{
  "manifest_version": 2,
  "name": "Joinchat - WhatsApp Contact Button",
  "version": "1.0",
  "description": "Quickly and easily access WhatsApp support for the pages you visit. Stop wasting time searching for a way to contact them when you need it.",
  "permissions": [
    "<all_urls>",
    "https://api.whatsapp.com/*",
    "https://wa.me/*"
  ],
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": false
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ],
      "css": [
        "styles.css"
      ]
    }
  ],
  "icons": {
    "16": "icons/icon16.png",
    "48": "icons/icon48.png",
    "128": "icons/icon128.png"
  },
  "browser_action": {
    "default_icon": {
      "16": "icons/icon16.png",
      "48": "icons/icon48.png",
      "128": "icons/icon128.png"
    },
    "default_title": "Joinchat"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "joinchat@join.chat",
      "strict_min_version": "140.0",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  }
}