Examine source code of YaMu

{
  "name": "YaMu",
  "description": "YaMu integrates Yandex.Music with MPRIS",
  "manifest_version": 2,
  "version": "2.1.1",
  "icons": {
    "16": "icons/yamu-16.png",
    "32": "icons/yamu-32.png",
    "48": "icons/yamu-48.png",
    "96": "icons/yamu-96.png",
    "128": "icons/yamu-128.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "yamu@0upti.me",
      "strict_min_version": "68.0"
    }
  },
  "applications": {
    "gecko": {
      "id": "yamu@0upti.me",
      "strict_min_version": "68.0"
    }
  },
  "key": "MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAzZLmNJxEsm37iSky47wAyRhAtNQe9WZpOujYRvxaZGzLtrqiMN7+lT2Nc6mL48RxVsczhSAPsEEHameHPFFInC0ACyPZVMqLeruj71+RHS0f+jbza3wuGwYateW3U+YtZTzsN4PYWEbI+b8hVqEyCqGL+KTMaAQnYI3z4rE6LwFTIk9iiW1D3zCzb7hmeJ6pZMDl2nDLqmsbndZidAMN0sMD/625d5RfC8k+TVgAu2+1lOeJ/etkAYQWKU2L3O/fQLIq/i9was8XoqGZComMQt4jawhXzui6/p2Tmc/peWYnorYePS/Yvy4BqKHMTjLqnsdTWclfIMeDwqiX3uPNJwIDAQAB",
  "content_scripts": [
    {
      "matches": [
        "*://music.yandex.ru/*",
        "*://radio.yandex.ru/*"
      ],
      "js": [
        "content.js"
      ]
    }
  ],
  "web_accessible_resources": [
    "page.js"
  ]
}