Examine source code of Word Count

{
  "manifest_version": 2,
  "name": "word count",
  "description": "Counts words and characters in selected text",
  "version": "2.1resigned1",
  "icons": {
    "32": "icons/icon_32.png",
    "48": "icons/icon_48.png",
    "64": "icons/icon_64.png"
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "permissions": [
    "menus",
    "notifications",
    "activeTab"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{5716fe2b-e871-4f3f-b8fc-b116971f152a}"
    }
  }
}