Examine source code of SongSphere

{
  "manifest_version": 2,
  "name": "SongSphere",
  "description": "Control every playing music tab from one popup - Spotify, YouTube Music, YouTube and more. Local-only, no analytics.",
  "version": "0.1.0",
  "icons": {
    "16": "icon/16.png",
    "19": "icon/19.png",
    "24": "icon/24.png",
    "32": "icon/32.png",
    "38": "icon/38.png",
    "48": "icon/48.png",
    "64": "icon/64.png",
    "96": "icon/96.png",
    "128": "icon/128.png"
  },
  "permissions": [
    "tabs",
    "activeTab",
    "scripting",
    "storage",
    "alarms",
    "https://open.spotify.com/*",
    "https://music.youtube.com/*",
    "https://www.youtube.com/*",
    "https://youtube.com/*",
    "https://m.youtube.com/*",
    "http://*/*",
    "https://*/*"
  ],
  "commands": {
    "toggle-play": {
      "suggested_key": {
        "default": "Alt+Shift+P",
        "mac": "Alt+Shift+P"
      },
      "description": "Play or pause"
    },
    "next-track": {
      "suggested_key": {
        "default": "Alt+Shift+Right",
        "mac": "Alt+Shift+Right"
      },
      "description": "Next track"
    },
    "previous-track": {
      "suggested_key": {
        "default": "Alt+Shift+Left",
        "mac": "Alt+Shift+Left"
      },
      "description": "Previous track"
    },
    "toggle-like": {
      "suggested_key": {
        "default": "Alt+Shift+L",
        "mac": "Alt+Shift+L"
      },
      "description": "Toggle like"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "songsphere@aaron.dev",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  },
  "web_accessible_resources": [
    "/songsphere-main-runtime.js"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_action": {
    "default_title": "SongSphere",
    "default_popup": "popup.html"
  },
  "content_scripts": [
    {
      "matches": [
        "*://*/*"
      ],
      "exclude_matches": [
        "*://m.youtube.com/*",
        "*://music.youtube.com/*",
        "*://open.spotify.com/*",
        "*://www.youtube.com/*",
        "*://youtube.com/*"
      ],
      "run_at": "document_start",
      "js": [
        "content-scripts/media.js"
      ]
    },
    {
      "matches": [
        "https://open.spotify.com/*"
      ],
      "run_at": "document_start",
      "js": [
        "content-scripts/spotify.js"
      ]
    },
    {
      "matches": [
        "https://m.youtube.com/*",
        "https://www.youtube.com/*",
        "https://youtube.com/*"
      ],
      "exclude_matches": [
        "https://music.youtube.com/*"
      ],
      "run_at": "document_start",
      "js": [
        "content-scripts/youtube.js"
      ]
    },
    {
      "matches": [
        "https://music.youtube.com/*"
      ],
      "run_at": "document_start",
      "js": [
        "content-scripts/ytmusic.js"
      ]
    }
  ]
}