Examine source code of Base64Extension

{
  "name": "Base64Extension",
  "version": "0.4resigned1",
  "description": "Decode base64 strings",
  "manifest_version": 2,
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": {
      "16": "images/img16.png",
      "32": "images/img32.png",
      "48": "images/img48.png",
      "128": "images/img128.png"
    }
  },
  "icons": {
    "16": "images/img16.png",
    "32": "images/img32.png",
    "48": "images/img48.png",
    "128": "images/img128.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{10ad5c0a-6356-44e1-95a8-d4335fbef589}"
    }
  }
}