Examine source code of Word Counter

{
  "manifest_version": 2,
  "name": "Word Counter",
  "version": "1.0",
  "description": "Counts the number of words on a webpage.",
  "permissions": [
    "activeTab"
  ],
  "browser_action": {
    "default_icon": {
      "48": "icon.png"
    },
    "default_popup": "popup.html"
  },
  "icons": {
    "48": "icon.png"
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{479bd66c-2cfb-4843-9c60-4a902009f2af}"
    }
  }
}