Examine source code of Word Counter Pro

{
  "manifest_version": 2,
  "name": "Word Counter",
  "version": "1.0",
  "description": "Counts the words and characters on your current webpage.",
  "icons": {
    "16": "images/icon16.png",
    "48": "images/icon48.png",
    "128": "images/icon128.png"
  },
  "permissions": [
    "activeTab",
    "<all_urls>"
  ],
  "background": {
    "scripts": [
      "scripts/background.js"
    ]
  },
  "browser_action": {
    "default_popup": "popup.html",
    "default_icons": {
      "16": "images/icon16.png",
      "48": "images/icon48.png",
      "128": "images/icon128.png"
    }
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "scripts/content.js"
      ]
    }
  ],
  "applications": {
    "gecko": {
      "id": "contact@cbd-certified.com",
      "strict_min_version": "42.0"
    }
  }
}