Examine source code of Audible Windows

{
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "permissions": [
    "tabs"
  ],
  "description": "Adds speaker icon to audible windows to indicate sound just like FireFox does natively for tabs",
  "manifest_version": 2,
  "name": "Audible Windows",
  "version": "1.0.2",
  "icons": {
    "48": "logo.png",
    "96": "logo.png"
  }
}