Examine source code of Keyboard Composer

{
  "manifest_version": 2,
  "name": "Keyboard Composer",
  "version": "1.0",
  "description": "Turn your computer keyboard into a daily-changing musical instrument mapping using Web Audio.",
  "icons": {
    "48": "icon-48.png",
    "128": "icon-128.png"
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content_script.js"
      ],
      "run_at": "document_idle"
    }
  ],
  "permissions": [
    "<all_urls>"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{ba0a4451-2bc7-4a53-9b1e-c1bb093bc0ca}"
    }
  }
}