Examine source code of Youtube SpeedWatch

{
  "manifest_version": 2,
  "name": "Youtube SpeedWatch",
  "description": "This extension shows the duration of a video on YouTube based on the playback speed.",
  "version": "1.3",
  "content_scripts": [
    {
      "matches": [
        "*://www.youtube.com/*"
      ],
      "js": [
        "script.js"
      ]
    }
  ],
  "icons": {
    "128": "icon.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{c0f53f92-7e34-409b-a494-1c1c84480624}"
    }
  }
}