Examine source code of Password Entropy Checker

{
  "manifest_version": 2,
  "name": "Password Entropy Checker",
  "version": "4.0.2",
  "description": "Check password strength, entropy and estimated crack time - fully offline, nothing is sent anywhere.",
  "browser_specific_settings": {
    "gecko": {
      "id": "{3bc5ff0a-7736-4081-b3b6-414a2fe1e0c4}",
      "strict_min_version": "123.0",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  },
  "permissions": [],
  "browser_action": {
    "default_icon": {
      "16": "assets/icons/icon16.png",
      "32": "assets/icons/icon32.png",
      "48": "assets/icons/icon48.png",
      "96": "assets/icons/icon96.png"
    },
    "default_title": "Password Entropy Checker",
    "default_popup": "src/popup.html"
  },
  "icons": {
    "16": "assets/icons/icon16.png",
    "32": "assets/icons/icon32.png",
    "48": "assets/icons/icon48.png",
    "96": "assets/icons/icon96.png"
  }
}