Examine source code of After Response

{
  "description": "Automatically save any requests and responses to your server, and modify the response to what you want.",
  "manifest_version": 2,
  "name": "After Response",
  "version": "3.2",
  "icons": {
    "48": "icons/ico_48.png",
    "64": "icons/ico_64.png",
    "128": "icons/ico_128.png"
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "permissions": [
    "tabs",
    "activeTab",
    "webRequest",
    "webRequestBlocking",
    "storage",
    "<all_urls>"
  ],
  "browser_action": {
    "default_icon": "icons/ico_48.png",
    "default_title": "After Response"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{ee113d05-dbb6-4943-9617-29761979fac6}"
    }
  }
}