Examine source code of Text Line Counter Panel

{
  "manifest_version": 2,
  "name": "Text Line Counter Panel",
  "version": "1.0.0",
  "description": "Count the number of lines in text.",
  "browser_action": {
    "default_title": "Line Counter",
    "default_popup": "popup.html"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "text-line-counter-1c7a5499-95d7-4b22-a983-e3ad789515bf@example.com",
      "strict_min_version": "58.0",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  }
}