Examine source code of Paragraph Length

{
  "manifest_version": 2,
  "name": "Paragraph Length",
  "version": "1.0",
  "description": "A professional tool to measure the length of selected paragraphs on a web page.",
  "icons": {
    "16": "icons/icon16.png",
    "48": "icons/icon48.png",
    "128": "icons/icon128.png"
  },
  "browser_action": {
    "default_icon": {
      "16": "icons/icon16.png",
      "48": "icons/icon48.png",
      "128": "icons/icon128.png"
    },
    "default_popup": "popup.html"
  },
  "permissions": [
    "activeTab"
  ],
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{f0de80d4-3ad3-4040-af5d-2c1ff8e05d16}"
    }
  }
}