Examine source code of Minimalist Toolbar

{
  "manifest_version": 2,
  "name": "Minimalist Toolbar",
  "version": "1.0",
  "description": "Automatically hides unnecessary buttons and menus on the toolbar when not in use, only leaving important features like the search box or back button. Other buttons appear when the user hovers over the toolbar.",
  "permissions": [
    "storage"
  ],
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": false
  },
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": {
      "48": "icons/icon48.png",
      "96": "icons/icon96.png"
    }
  },
  "icons": {
    "48": "icons/icon48.png",
    "96": "icons/icon96.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{d2144751-aec4-4b13-90ad-0062a093d35d}"
    }
  }
}