Examine source code of oli-node-counter

{
  "description": "Dom Node Counter",
  "manifest_version": 2,
  "name": "oli-node-counter",
  "version": "1.0",
  "author": "Kushan Gunasinghe",
  "homepage_url": "https://addons.mozilla.org/it/firefox/user/kushan4157/",
  "icons": {
    "48": "icons/icon-48.png",
    "64": "icons/icon-64.png",
    "128": "icons/icon-128.png"
  },
  "permissions": [
    "<all_urls>"
  ],
  "devtools_page": "devtools/SidebarPane.html"
}