Examine source code of ThemeShuffler

{
  "background": {
    "scripts": [
      "main.js",
      "background.js"
    ],
    "persistent": false
  },
  "version": "0.9",
  "description": "Automatically changes your theme at startup then every hours to any theme you have downloaded. Default theme, dark theme, and light theme will not be selected.",
  "manifest_version": 2,
  "name": "Theme change randomizer",
  "summary": "Changes your theme automatically when you load Firefox then every hours",
  "permissions": [
    "management",
    "alarms",
    "storage"
  ],
  "icons": {
    "48": "logo.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "themeshuffler@bouns.com"
    }
  },
  "options_ui": {
    "page": "options.html",
    "open_in_tab": true
  },
  "browser_action": {
    "default_popup": "options.html",
    "default_icon": "logo.png"
  }
}