Examine source code of Codeforces++

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  "description": "Codeforces extension pack",
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    "tabs //",
    "*://codeforces.com/*",
    "http://fonts.googleapis.com/*",
    "https://fonts.googleapis.com/*"
  ],
  "content_scripts": [
    {
      "matches": [
        "*://codeforces.com/*"
      ],
      "js": [
        "browser-polyfill.min.js",
        "contentScript.js"
      ],
      "css": [
        "common.css"
      ],
      "run_at": "document_start"
    }
  ],
  "web_accessible_resources": [
    "*.js"
  ],
  "background": {
    "persistent": false,
    "scripts": [
      "browser-polyfill.min.js",
      "background.js"
    ]
  },
  "browser_action": {
    "default_popup": "popup.html",
    "default_title": "Codeforces++"
  },
  "icons": {
    "16": "icons/16x16.png",
    "32": "icons/32x32.png",
    "48": "icons/48x48.png",
    "128": "icons/128x128.png"
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}