Examine source code of Word Count

{
  "manifest_version": 2,
  "name": "Word Count",
  "version": "1.0",
  "description": "Displays the number of characters on the current web page.",
  "browser_action": {
    "default_icon": "icon.png"
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content_script.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{d8f86979-6c2a-46ee-98f8-094a7f01718e}"
    }
  }
}