Examine source code of Fuel Prices for Maps

{
  "manifest_version": 3,
  "name": "Fuel Prices for Maps",
  "description": "Show route fuel cost in Google Maps with average fuel prices per country.",
  "version": "1.1.1",
  "icons": {
    "16": "/icon/16.png",
    "32": "/icon/32.png",
    "48": "/icon/48.png",
    "96": "/icon/96.png",
    "128": "/icon/128.png"
  },
  "permissions": [
    "storage"
  ],
  "host_permissions": [
    "https://www.google.com/maps/*",
    "https://maps.google.com/*",
    "https://fuel.kyzegs.com/*"
  ],
  "action": {
    "default_title": "Fuel Cost",
    "default_popup": "popup.html",
    "default_icon": {
      "16": "/icon/16.png",
      "32": "/icon/32.png"
    }
  },
  "options_ui": {
    "open_in_tab": false,
    "page": "options.html"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "fuel-cost-for-maps@example.com",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "https://maps.google.com/*",
        "https://www.google.com/maps/*"
      ],
      "css": [
        "content-scripts/content.css"
      ],
      "js": [
        "content-scripts/content.js"
      ]
    }
  ]
}