Examine source code of Text Word Frequency Panel

{
  "manifest_version": 2,
  "name": "Text Word Frequency Panel",
  "version": "1.0.0",
  "description": "Count how many times each word appears in a text.",
  "browser_action": {
    "default_title": "Word Frequency",
    "default_popup": "popup.html"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "text-word-frequency-18dccb85-de62-4863-a729-caea27f6fd61@example.com",
      "strict_min_version": "58.0",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  }
}