Examine source code of Spotify Playback Speed

{
  "name": "Spotify Playback Speed",
  "description": "Adds a button and menu to manipulate playback speed on Spotify Web.",
  "version": "1.13",
  "manifest_version": 2,
  "author": "@rnikko",
  "icons": {
    "16": "icons/icon16.png",
    "48": "icons/icon48.png",
    "64": "icons/icon64.png",
    "128": "icons/icon128.png"
  },
  "content_scripts": [
    {
      "matches": [
        "https://open.spotify.com/*"
      ],
      "js": [
        "content-script.js"
      ]
    }
  ],
  "web_accessible_resources": [
    "script.js"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{a34e6974-7b0f-46a8-9092-a970cd732422}"
    }
  }
}