Examine source code of Mail Checker for Gmail

{
  "manifest_version": 3,
  "name": "__MSG_gmailcheck_name__",
  "version": "0.1",
  "description": "__MSG_gmailcheck_description__",
  "default_locale": "en",
  "browser_specific_settings": {
    "gecko": {
      "id": "easygmailchecker@extension.local",
      "strict_min_version": "142.0",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  },
  "action": {
    "default_icon": "gmail_not_logged_in.png"
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "host_permissions": [
    "*://*.google.com/",
    "https://mail.google.com/"
  ],
  "permissions": [
    "storage",
    "alarms",
    "tabs",
    "webNavigation"
  ],
  "icons": {
    "128": "icon_128.png"
  }
}