Examine source code of Word Counter

{
  "manifest_version": 2,
  "name": "Word Counter",
  "version": "1.0",
  "description": "Counts the number of words on the current web page.",
  "permissions": [
    "activeTab"
  ],
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": false
  },
  "browser_action": {
    "default_popup": "popup.html",
    "default_title": "Word Counter"
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{6839a2bf-180f-4b1c-a392-766dd6c8d5b3}"
    }
  }
}