Examine source code of Form Typing Rhythm

{
  "manifest_version": 2,
  "name": "Form Typing Rhythm",
  "version": "1.0",
  "description": "Plays musical sounds while typing in form fields: letters=piano, space=kick, enter=cymbal, backspace=soft clap.",
  "permissions": [
    "<all_urls>"
  ],
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ],
      "css": [
        "style.css"
      ],
      "run_at": "document_idle"
    }
  ],
  "icons": {
    "48": "icon.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{c238116e-a2f5-4097-be9a-60973b9bd1a7}"
    }
  }
}