Examine source code of Current Song Overlay

{
  "manifest_version": 2,
  "name": "CurrentSong",
  "version": "0.5.1",
  "description": "Implements a client to send the current active tab to a local server",
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "*://*.youtube.com/*"
      ],
      "js": [
        "content-scripts/trackVideoProgress.js"
      ],
      "all_frames": true
    },
    {
      "matches": [
        "*://*.soundcloud.com/*"
      ],
      "js": [
        "content-scripts/soundcloud.js"
      ]
    },
    {
      "matches": [
        "*://*.neverthink.tv/*"
      ],
      "js": [
        "content-scripts/neverthink.js"
      ]
    },
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content-scripts/mediaSessionProxy.js"
      ],
      "run_at": "document_start",
      "all_frames": true
    }
  ],
  "web_accessible_resources": [
    "content-scripts/mediaSessionProxy.inject.js"
  ],
  "permissions": [
    "tabs"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{02914143-ede8-492c-8ad4-8a3af03f75bb}",
      "strict_min_version": "78.0"
    }
  }
}