Examine source code of NWS!F2C

{
  "manifest_version": 3,
  "name": "NWS!F2C",
  "version": "1.1",
  "description": "Converts Fahrenheit temperatures to Celsius on forecast.weather.gov/MapClick.php.",
  "icons": {
    "48": "icons/icon-48.png"
  },
  "content_scripts": [
    {
      "matches": [
        "*://forecast.weather.gov/MapClick.php*"
      ],
      "js": [
        "content.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{b2da0ddb-1cb2-4baf-a8b4-30bd515e5e12}"
    }
  }
}