Examine source code of CFTIMER

{
  "content_scripts": [
    {
      "js": [
        "script.js"
      ],
      "matches": [
        "*://codeforces.com/*"
      ],
      "css": [
        "style.css"
      ]
    }
  ],
  "name": "Timely",
  "version": "0.0.1",
  "manifest_version": 2,
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": "hourglass.png"
  },
  "permissions": [
    "tabs",
    "storage"
  ],
  "icons": {
    "128": "hourglass.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{7904ca2b-e628-4a97-8b37-4d693a431b2f}"
    }
  }
}