Examine source code of Clock: Hours

{
  "manifest_version": 2,
  "name": "Clock: Hours",
  "version": "1.1",
  "description": "Adds hour part of clock in Toolbar",
  "icons": {
    "48": "icon48.png",
    "96": "icon96.png"
  },
  "browser_action": {
    "default_icon": "none.png",
    "default_title": "Hours"
  },
  "background": {
    "scripts": [
      "badge-clock.js"
    ]
  },
  "permissions": [
    "storage"
  ],
  "options_ui": {
    "page": "options.html"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{3888b6ff-d555-4801-9afb-f916dfd3e6d5}"
    }
  }
}