Examine source code of Theme Toggler v2

{
  "manifest_version": 2,
  "name": "Theme Toggler",
  "version": "1.0",
  "description": "Toggle between light and dark themes for Firefox.",
  "permissions": [
    "theme"
  ],
  "browser_action": {
    "default_icon": "icons/theme-toggle-48.png",
    "default_popup": "popup.html",
    "default_title": "Toggle Theme"
  },
  "icons": {
    "48": "icons/theme-toggle-48.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{66ba00c4-0dfc-4d74-a6b4-4ef888f43068}"
    }
  }
}