Examine source code of Theme Creator

{
  "manifest_version": 2,
  "name": "Theme Creator",
  "version": "1.0.0",
  "description": "Simple Theme Creator for Firefox: pick colors, preview, export as a WebExtension theme (manifest.json snippet). Stores user themes locally.",
  "permissions": [
    "storage"
  ],
  "browser_action": {
    "default_title": "Theme Creator",
    "default_popup": "creator.html"
  },
  "options_ui": {
    "page": "options.html",
    "open_in_tab": true
  },
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": false
  },
  "content_security_policy": "script-src 'self'; object-src 'self'",
  "browser_specific_settings": {
    "gecko": {
      "id": "{f139997c-8073-4da9-99ef-c3e7b68687b5}"
    }
  }
}