Examine source code of CF Stopwatch

{
  "manifest_version": 2,
  "name": "CF Stopwatch",
  "version": "1.0.0",
  "description": "Automatically tracks how long you spend on each Codeforces problem. Stops on Accepted, survives tab switches, and lets you reattempt with one click.",
  "browser_specific_settings": {
    "gecko": {
      "id": "cf-stopwatch@extension",
      "strict_min_version": "140.0",
      "data_collection_permissions": {
        "required": [
          "none"
        ],
        "optional": []
      }
    }
  },
  "permissions": [
    "storage",
    "*://codeforces.com/*"
  ],
  "content_scripts": [
    {
      "matches": [
        "*://codeforces.com/problemset/problem/*/*",
        "*://codeforces.com/contest/*/problem/*",
        "*://codeforces.com/gym/*/problem/*"
      ],
      "js": [
        "content.js"
      ],
      "css": [
        "content.css"
      ],
      "run_at": "document_idle"
    }
  ],
  "browser_action": {
    "default_title": "CF Stopwatch",
    "default_icon": {
      "46": "icon46.png",
      "96": "icon96.png"
    }
  },
  "icons": {
    "46": "icon46.png",
    "96": "icon96.png"
  }
}