Examine source code of Simple Word Counter

{
  "manifest_version": 2,
  "name": "Simple Word Counter",
  "version": "1.0",
  "description": "A simple word counter extension.",
  "permissions": [
    "clipboardRead"
  ],
  "icons": {
    "16": "icons/icon16.png",
    "32": "icons/icon32.png",
    "48": "icons/icon48.png",
    "64": "icons/icon64.png",
    "128": "icons/icon128.png"
  },
  "background": {
    "scripts": [
      "countWords.js"
    ]
  },
  "browser_action": {
    "default_popup": "popup.html"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{3ab3f880-f349-4656-a4cf-b184734d3a4b}"
    }
  }
}