Examine source code of Tagada for Gmail

{
  "name": "__MSG_extName__",
  "description": "__MSG_extDescription__",
  "version": "1.3.14",
  "manifest_version": 3,
  "background": {
    "scripts": [
      "js/background.min.js"
    ]
  },
  "permissions": [
    "storage"
  ],
  "default_locale": "en",
  "action": {
    "default_icon": {
      "16": "images/icon_16.png",
      "32": "images/icon_32.png"
    }
  },
  "icons": {
    "16": "images/icon_16.png",
    "32": "images/icon_32.png",
    "48": "images/icon_48.png",
    "128": "images/icon_128.png"
  },
  "web_accessible_resources": [
    {
      "resources": [
        "images/steps.png",
        "images/logo_512.png",
        "images/onboarding-1.gif",
        "images/onboarding-2.gif",
        "images/onboarding-3.gif",
        "images/onboarding-4.gif",
        "_locales/fr/messages.json",
        "_locales/en/messages.json",
        "html/login.html",
        "html/settings.html",
        "html/account.html",
        "html/onboarding.html",
        "html/loader.html"
      ],
      "matches": [
        "https://mail.google.com/*",
        "https://app.tagada.pro/*"
      ]
    }
  ],
  "content_scripts": [
    {
      "matches": [
        "https://mail.google.com/*",
        "https://app.tagada.pro/*"
      ],
      "css": [
        "css/main.min.css"
      ],
      "js": [
        "js/tagada.min.js",
        "js/sortable.min.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "hello@tagada.pro",
      "data_collection_permissions": {
        "required": [
          "personallyIdentifyingInfo",
          "authenticationInfo"
        ],
        "optional": [
          "technicalAndInteraction"
        ]
      }
    }
  }
}