Examine source code of SiteSentry v2

{
  "manifest_version": 2,
  "name": "SiteSentry",
  "version": "1.0",
  "description": "Block sites and enhance your productivity with customizable limiting techniques and features. All for free.",
  "icons": {
    "48": "icon.png"
  },
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": "icon.png"
  },
  "permissions": [
    "storage"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{924b8ed3-fcbc-46e3-a5e5-24cd0d083cdd}"
    }
  }
}