Examine source code of RouteEstimate

{
  "manifest_version": 2,
  "name": "RouteEstimate",
  "version": "1.1.4",
  "description": "Calculate estimated fuel cost for a route on Google Maps.",
  "permissions": [
    "storage",
    "https://www.google.com/maps/*"
  ],
  "browser_action": {
    "default_popup": "views/popup-firefox.html",
    "default_icon": {
      "16": "assets/icons/icon16.png",
      "32": "assets/icons/icon32.png",
      "48": "assets/icons/icon48.png",
      "64": "assets/icons/icon64.png",
      "128": "assets/icons/icon128.png",
      "212": "assets/icons/icon212.png"
    }
  },
  "content_scripts": [
    {
      "matches": [
        "https://www.google.com/maps/*"
      ],
      "js": [
        "content/content.js"
      ]
    }
  ],
  "icons": {
    "16": "assets/icons/icon16.png",
    "32": "assets/icons/icon32.png",
    "48": "assets/icons/icon48.png",
    "64": "assets/icons/icon64.png",
    "128": "assets/icons/icon128.png",
    "212": "assets/icons/icon212.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{1c2d281c-bc70-4116-acac-2192468ba87e}"
    }
  }
}