Examine source code of Focus Idle City

{
  "name": "Focus Idle City",
  "version": "0.7",
  "description": "Focus on what's important.",
  "manifest_version": 2,
  "browser_action": {
    "default_popup": "index.html"
  },
  "permissions": [
    "notifications",
    "<all_urls>",
    "tabs"
  ],
  "background": {
    "scripts": [
      "background-script.js"
    ]
  },
  "icons": {
    "16": "icon-16.png",
    "48": "icon-48.png",
    "128": "icon-128.png"
  }
}