Examine source code of Close Inactive Tabs

{
  "manifest_version": 2,
  "name": "close-inactive-tabs",
  "version": "1.0.4",
  "description": "This extension closes tabs that have been inactive for more than 90 days.",
  "content_security_policy": "script-src 'self'; object-src 'self'",
  "icons": {
    "474": "icon.jpg"
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_action": {
    "default_icon": {
      "474": "icon.jpg"
    },
    "default_title": "Inactive Tabs",
    "default_popup": "popup.html"
  },
  "options_ui": {
    "page": "settings.html"
  },
  "permissions": [
    "tabs",
    "notifications",
    "browser_action",
    "storage"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "close-inactive-tabs@example.com"
    }
  }
}