Examine source code of Letter Count Panel

{
  "manifest_version": 2,
  "name": "Letter Count Panel",
  "version": "1.0.0",
  "description": "A small popup that counts letters in text.",
  "browser_action": {
    "default_title": "Letter Count",
    "default_popup": "popup.html"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "letter-count-6d15404b-fecc-4687-986c-56111e3f530e@example.com",
      "strict_min_version": "58.0",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  }
}