Examine source code of Zoom Page Size

{
  "manifest_version": 2,
  "name": "Text Zoom",
  "version": "1.0",
  "description": "Zoom in or out on the text of any website and reset to original size",
  "icons": {
    "48": "icon.png"
  },
  "permissions": [
    "activeTab"
  ],
  "browser_action": {
    "default_title": "Text Zoom",
    "default_popup": "popup.html"
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{b56fe212-555c-4deb-b451-4eeae90c429d}"
    }
  }
}