Examine source code of Quick Line Counter Panel

{
  "manifest_version": 2,
  "name": "Quick Line Counter Panel",
  "version": "1.0.0",
  "description": "A small popup that counts lines of pasted text.",
  "browser_action": {
    "default_title": "Line Counter",
    "default_popup": "popup.html"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "quick-line-counter-6d77dda4-fe78-4dc3-812f-c4592612ec9d@example.com",
      "strict_min_version": "58.0",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  }
}