Examine source code of keygen music play button

{
  "name": "__MSG_extName__",
  "description": "__MSG_extDescr__",
  "version": "3.0.1resigned1",
  "manifest_version": 2,
  "default_locale": "en",
  "icons": {
    "16": "img/ext_icons/16.png",
    "48": "img/ext_icons/48.png",
    "128": "img/ext_icons/128.png"
  },
  "browser_action": {
    "default_icon": {
      "19": "img/ext_icons/19_stop.png",
      "38": "img/ext_icons/38.png"
    },
    "default_title": "__MSG_p_defaultTitle__"
  },
  "background": {
    "scripts": [
      "js/background.js"
    ]
  },
  "permissions": [
    "http://keygenmusic.tk/*"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "@keygen-music-play-button"
    }
  }
}