Examine source code of YouTube Music Control

{
  "manifest_version": 2,
  "name": "Youtube Music Control",
  "version": "1.3.3",
  "description": "Control Youtube music tab from other tabs.",
  "icons": {
    "48": "icons/ytMusicIcon.png"
  },
  "content_scripts": [
    {
      "matches": [
        "*://music.youtube.com/*"
      ],
      "js": [
        "yt-music-control.js"
      ]
    }
  ],
  "browser_action": {
    "default_icon": {
      "48": "icons/ytMusicIcon.png"
    },
    "default_popup": "popup/index.html"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{4a5cfa88-e573-4524-8107-c4c2a0897bb9}"
    }
  }
}