Examine source code of Media Key Manager

{
  "manifest_version": 2,
  "short_name": "__MSG_extensionName__",
  "name": "__MSG_extensionName__",
  "version": "2.5.2",
  "description": "__MSG_extensionDescription__",
  "icons": {
    "64": "icon64.png",
    "128": "icon128.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{176129d5-ddb5-37bb-5620-bc6d2489e859}",
      "strict_min_version": "129.0"
    }
  },
  "background": {
    "page": "index.html"
  },
  "commands": {
    "MediaPlayPause": {
      "description": "toggles play state of the last active media website",
      "suggested_key": {
        "default": "MediaPlayPause"
      },
      "global": true
    },
    "MediaNextTrack": {
      "description": "plays the next track for the last active media website",
      "suggested_key": {
        "default": "MediaNextTrack"
      },
      "global": true
    },
    "MediaPrevTrack": {
      "description": "plays the previous track for the last active media website",
      "suggested_key": {
        "default": "MediaPrevTrack"
      },
      "global": true
    },
    "MediaStop": {
      "description": "stops playback of the last active media website",
      "suggested_key": {
        "default": "MediaStop"
      },
      "global": true
    }
  },
  "options_ui": {
    "page": "options/options_ui.html",
    "browser_style": false,
    "chrome_style": false,
    "open_in_tab": false
  },
  "permissions": [
    "storage"
  ],
  "optional_permissions": [
    "*://*/"
  ],
  "content_scripts": [
    {
      "matches": [
        "*://*.youtube.com/*"
      ],
      "js": [
        "lib/browser-polyfill.min.js",
        "data/youtube.com-orchestrator.js"
      ],
      "all_frames": true
    },
    {
      "js": [
        "lib/browser-polyfill.min.js",
        "data/pandora.com-view.js",
        "data/finder.js",
        "data/orchestrator.js"
      ],
      "matches": [
        "*://*.pandora.com/*"
      ]
    },
    {
      "js": [
        "lib/browser-polyfill.min.js",
        "data/tidal.com-view.js",
        "data/finder.js",
        "data/orchestrator.js"
      ],
      "matches": [
        "*://*.tidal.com/*"
      ]
    },
    {
      "js": [
        "lib/browser-polyfill.min.js",
        "data/music.apple.com-view.js",
        "data/finder.js",
        "data/orchestrator.js"
      ],
      "matches": [
        "*://*.music.apple.com/*"
      ]
    },
    {
      "js": [
        "lib/browser-polyfill.min.js",
        "data/bandcamp.com-view.js",
        "data/finder.js",
        "data/orchestrator.js"
      ],
      "matches": [
        "*://*.bandcamp.com/*",
        "*://shop.attackthemusic.com/*"
      ]
    },
    {
      "js": [
        "lib/browser-polyfill.min.js",
        "data/play.google.com-view.js",
        "data/finder.js",
        "data/orchestrator.js"
      ],
      "matches": [
        "*://*.play.google.com/*"
      ]
    },
    {
      "js": [
        "lib/browser-polyfill.min.js",
        "data/play.spotify.com-view.js",
        "data/finder.js",
        "data/orchestrator.js"
      ],
      "matches": [
        "*://*.play.spotify.com/*"
      ]
    },
    {
      "js": [
        "lib/browser-polyfill.min.js",
        "data/player.spotify.com-view.js",
        "data/finder.js",
        "data/orchestrator.js"
      ],
      "matches": [
        "*://*.player.spotify.com/*"
      ]
    },
    {
      "js": [
        "lib/browser-polyfill.min.js",
        "data/open.spotify.com-view.js",
        "data/finder.js",
        "data/orchestrator.js"
      ],
      "matches": [
        "*://*.open.spotify.com/*"
      ]
    },
    {
      "js": [
        "lib/browser-polyfill.min.js",
        "data/soundcloud.com-view.js",
        "data/finder.js",
        "data/orchestrator.js"
      ],
      "matches": [
        "*://soundcloud.com/*"
      ]
    },
    {
      "matches": [
        "https://w.soundcloud.com/player/*"
      ],
      "all_frames": true,
      "js": [
        "lib/browser-polyfill.min.js",
        "data/w.soundcloud.com-orchestrator.js"
      ]
    },
    {
      "js": [
        "lib/browser-polyfill.min.js",
        "data/stitcher.com-view.js",
        "data/finder.js",
        "data/orchestrator.js"
      ],
      "matches": [
        "*://app.stitcher.com/*"
      ]
    },
    {
      "js": [
        "lib/browser-polyfill.min.js",
        "data/music.yandex.ru-view.js",
        "data/finder.js",
        "data/orchestrator.js"
      ],
      "matches": [
        "*://*.music.yandex.ru/*"
      ]
    },
    {
      "js": [
        "lib/browser-polyfill.min.js",
        "data/vk.com-view.js",
        "data/finder.js",
        "data/orchestrator.js"
      ],
      "matches": [
        "*://*.vk.com/*"
      ]
    },
    {
      "js": [
        "lib/browser-polyfill.min.js",
        "data/radio.yandex.ru-view.js",
        "data/finder.js",
        "data/orchestrator.js"
      ],
      "matches": [
        "*://*.radio.yandex.ru/*"
      ]
    },
    {
      "js": [
        "lib/browser-polyfill.min.js",
        "data/deezer.com-view.js",
        "data/finder.js",
        "data/orchestrator.js"
      ],
      "matches": [
        "*://*.deezer.com/*"
      ]
    },
    {
      "js": [
        "lib/browser-polyfill.min.js",
        "data/overcast.fm-view.js",
        "data/finder.js",
        "data/orchestrator.js"
      ],
      "matches": [
        "*://*.overcast.fm/*"
      ]
    },
    {
      "js": [
        "lib/browser-polyfill.min.js",
        "data/plex.tv-view.js",
        "data/finder.js",
        "data/orchestrator.js"
      ],
      "matches": [
        "*://*.plex.tv/*"
      ]
    },
    {
      "js": [
        "lib/browser-polyfill.min.js",
        "data/pluralsight.com-view.js",
        "data/finder.js",
        "data/orchestrator.js"
      ],
      "matches": [
        "*://*.app.pluralsight.com/*"
      ]
    },
    {
      "js": [
        "lib/browser-polyfill.min.js",
        "data/jamstash-view.js",
        "data/finder.js",
        "data/orchestrator.js"
      ],
      "matches": [
        "*://*.jamstash.com/*"
      ]
    },
    {
      "js": [
        "lib/browser-polyfill.min.js",
        "data/jango.com-view.js",
        "data/finder.js",
        "data/orchestrator.js"
      ],
      "matches": [
        "*://*.jango.com/*"
      ]
    },
    {
      "js": [
        "lib/browser-polyfill.min.js",
        "data/kanopy-view.js",
        "data/finder.js",
        "data/orchestrator.js"
      ],
      "matches": [
        "*://*.kanopy.com/*"
      ]
    },
    {
      "js": [
        "lib/browser-polyfill.min.js",
        "data/koel-view.js",
        "data/finder.js",
        "data/orchestrator.js"
      ],
      "matches": [
        "*://*.koel.phanan.net/*"
      ]
    },
    {
      "js": [
        "lib/browser-polyfill.min.js",
        "data/subsonic-view.js",
        "data/finder.js",
        "data/orchestrator.js"
      ],
      "matches": [
        "*://*.demo.subsonic.org/*"
      ]
    },
    {
      "js": [
        "lib/browser-polyfill.min.js",
        "data/madsonic-view.js",
        "data/finder.js",
        "data/orchestrator.js"
      ],
      "matches": [
        "*://*.demo.madsonic.org/*"
      ]
    },
    {
      "js": [
        "lib/browser-polyfill.min.js",
        "data/music.amazon-view.js",
        "data/finder.js",
        "data/orchestrator.js"
      ],
      "matches": [
        "*://*.music.amazon.com/*",
        "*://*.music.amazon.de/*",
        "*://*.music.amazon.co.uk/*"
      ]
    },
    {
      "js": [
        "lib/browser-polyfill.min.js",
        "data/cbcmusic.ca-view.js",
        "data/finder.js",
        "data/orchestrator.js"
      ],
      "matches": [
        "*://*.cbcmusic.ca/*"
      ]
    },
    {
      "js": [
        "lib/browser-polyfill.min.js",
        "data/mixcloud.com-view.js",
        "data/finder.js",
        "data/orchestrator.js"
      ],
      "matches": [
        "*://*.mixcloud.com/*"
      ]
    },
    {
      "js": [
        "lib/browser-polyfill.min.js",
        "data/hulu.com-view.js",
        "data/finder.js",
        "data/orchestrator.js"
      ],
      "matches": [
        "*://*.hulu.com/*"
      ]
    },
    {
      "js": [
        "lib/browser-polyfill.min.js",
        "data/hypem.com-view.js",
        "data/finder.js",
        "data/orchestrator.js"
      ],
      "matches": [
        "*://*.hypem.com/*"
      ]
    },
    {
      "js": [
        "lib/browser-polyfill.min.js",
        "data/netflix.com-view.js",
        "data/finder.js",
        "data/orchestrator.js"
      ],
      "matches": [
        "*://*.netflix.com/*"
      ]
    },
    {
      "js": [
        "lib/browser-polyfill.min.js",
        "data/npr.org-view.js",
        "data/finder.js",
        "data/orchestrator.js"
      ],
      "matches": [
        "*://*.npr.org/*"
      ]
    },
    {
      "js": [
        "lib/browser-polyfill.min.js",
        "data/tunein.com-view.js",
        "data/finder.js",
        "data/orchestrator.js"
      ],
      "matches": [
        "*://*.tunein.com/*"
      ]
    },
    {
      "js": [
        "lib/browser-polyfill.min.js",
        "data/play.pocketcasts.com-view.js",
        "data/finder.js",
        "data/orchestrator.js"
      ],
      "matches": [
        "*://play.pocketcasts.com/*"
      ]
    },
    {
      "js": [
        "lib/browser-polyfill.min.js",
        "data/di.fm-view.js",
        "data/finder.js",
        "data/orchestrator.js"
      ],
      "matches": [
        "*://*.di.fm/*"
      ]
    },
    {
      "js": [
        "lib/browser-polyfill.min.js",
        "data/udemy.com-view.js",
        "data/finder.js",
        "data/orchestrator.js"
      ],
      "matches": [
        "*://*.udemy.com/*"
      ]
    }
  ],
  "web_accessible_resources": [
    "data/youtube.com-orchestrator-pageScript.js"
  ]
}