Examine source code of Force Dark Mode

{
  "manifest_version": 2,
  "name": "Force Darkmode",
  "version": "1.0",
  "description": "Forces darkmode to any website (will become cursed in some websites.)",
  "icons": {
    "48": "icons/48.png"
  },
  "permissions": [
    "activeTab"
  ],
  "browser_action": {
    "default_icon": "icons/48.png",
    "default_title": "Force Darkmode",
    "default_popup": "popup/settings.html"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{43c448cf-4ed4-4611-acd9-5072d7241682}"
    }
  }
}