Examine source code of Price to Hours

{
  "manifest_version": 2,
  "name": "Price to Hours",
  "version": "1.0",
  "description": "Translates prices to your time",
  "icons": {
    "48": "images/alarm-clock.svg",
    "96": "images/alarm-clock.svg",
    "512": "images/alarm-clock.svg"
  },
  "permissions": [
    "activeTab",
    "storage"
  ],
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "real-cost.js"
      ]
    }
  ],
  "browser_action": {
    "default_title": "Price to Hours",
    "default_popup": "menu.html"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{5e9b3c10-ca8a-4d9c-aec5-aff2ca2a7863}"
    }
  }
}