Examine source code of Switch to audible tab

{
  "manifest_version": 2,
  "name": "Switch to audible tab",
  "version": "0.0.9",
  "description": "Focus on tab that is currently making sound (Alt+Shift+A).",
  "icons": {
    "128": "img/128.png"
  },
  "background": {
    "scripts": [
      "src/background.js"
    ]
  },
  "options_ui": {
    "page": "static/settings.html",
    "browser_style": false,
    "open_in_tab": false
  },
  "browser_action": {
    "default_icon": {
      "128": "img/128.png"
    },
    "default_title": "Switch to audible tab (Alt+Shift+A)"
  },
  "commands": {
    "_execute_browser_action": {
      "suggested_key": {
        "default": "Alt+Shift+A"
      }
    }
  },
  "permissions": [
    "tabs",
    "storage",
    "menus",
    "activeTab"
  ],
  "applications": {
    "gecko": {
      "id": "{0cd726db-f954-44f2-bf4f-7ed0de734de2}",
      "strict_min_version": "57.0"
    }
  }
}