Examine source code of Price2Time

{
  "description": "Give you knowledge about how much cost of your time to buy a product",
  "manifest_version": 2,
  "name": "Price2Time",
  "version": "1.0.4",
  "homepage_url": "https://github.com/jsonzilla/price_to_time/",
  "icons": {
    "48": "icons/icon-48.png"
  },
  "content_scripts": [
    {
      "matches": [
        "*://*.amazon.com.br/*",
        "*://*.amazon.com/*",
        "*://*.mercadolivre.com.br/*",
        "*://*.submarino.com.br/*"
      ],
      "js": [
        "price2time.js"
      ]
    }
  ],
  "options_ui": {
    "page": "options/options.html"
  },
  "permissions": [
    "storage"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "cardos.jeison@gmail.com",
      "strict_min_version": "57.0"
    }
  }
}