Examine source code of SoundControl

{
  "manifest_version": 2,
  "name": "SoundControl",
  "version": "1.0.1",
  "description": "Controla y ecualiza el sonido en Firefox",
  "permissions": [
    "activeTab",
    "storage",
    "<all_urls>"
  ],
  "browser_action": {
    "default_popup": "popup/popup.html",
    "default_icon": {
      "16": "icons/soundcontrol16.png",
      "48": "icons/soundcontrol48.png",
      "128": "icons/soundcontrol128.png"
    }
  },
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": false
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content_scripts/soundcontrol.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{a4069155-aeae-40ad-be7a-26ec54b89549}"
    }
  }
}