Examine source code of Page Timeout Closer

{
  "manifest_version": 2,
  "name": "Page Timeout Closer",
  "version": "1.0",
  "description": "Automatically close inactive tabs after a chosen time",
  "permissions": [
    "tabs",
    "storage",
    "alarms"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{d0b62351-41d0-43d4-849e-44e7df2cbd5c}",
      "strict_min_version": "120.0"
    }
  },
  "icons": {
    "64": "icon64.png",
    "128": "icon128.png"
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_action": {
    "default_title": "Page Timeout Closer",
    "default_popup": "popup.html",
    "default_icon": {
      "64": "icon64.png",
      "128": "icon128.png"
    }
  }
}