Examine source code of PopupButton

{
  "manifest_version": 2,
  "name": "popupButton57",
  "version": "0.0.4resigned1",
  "description": "Turn popups on/off by clicking a button",
  "icons": {
    "16": "data/icon-16.png",
    "32": "data/icon-32.png",
    "64": "data/icon-64.png"
  },
  "permissions": [
    "browserSettings"
  ],
  "browser_action": {
    "default_icon": "data/icon-32.png",
    "default_title": "Turn Popups on/off"
  },
  "background": {
    "scripts": [
      "index.js"
    ]
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "@popupbutton"
    }
  }
}