Examine source code of Exam Countdown

{
  "name": "Exam Countdown",
  "description": "A New Tab Countdown Extension",
  "version": "1.4.1",
  "browser_specific_settings": {
    "gecko": {
      "id": "support@novatra.in"
    }
  },
  "author": "SpreadSheets600",
  "manifest_version": 2,
  "icons": {
    "16": "icons/icon16.png",
    "32": "icons/icon32.png",
    "48": "icons/icon48.png",
    "96": "icons/icon96.png",
    "128": "icons/icon128.png"
  },
  "browser_action": {
    "default_popup": "popup/popup.html",
    "default_title": "Exam Countdown"
  },
  "background": {
    "scripts": [
      "background/background.js"
    ],
    "persistent": false
  },
  "permissions": [
    "storage",
    "activeTab"
  ],
  "content_scripts": [
    {
      "matches": [
        "*://www.youtube.com/*",
        "*://m.youtube.com/*"
      ],
      "js": [
        "content/youtube-unhook.js"
      ],
      "run_at": "document_idle"
    },
    {
      "matches": [
        "http://*/*",
        "https://*/*"
      ],
      "js": [
        "content/site-blocker.js"
      ],
      "run_at": "document_start"
    }
  ],
  "web_accessible_resources": [
    "blocker-settings.css"
  ],
  "chrome_url_overrides": {
    "newtab": "newtab/newtab.html"
  },
  "content_security_policy": "script-src 'self'; object-src 'self'"
}