Examine source code of Gradient Explorer

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  "description": "__MSG_extensionDescription__",
  "version": "1.0",
  "manifest_version": 2,
  "action": {
    "default_popup": "index.html"
  },
  "icons": {
    "16": "icons/icon16.png",
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    "48": "icons/icon48.png",
    "128": "icons/icon128.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{35f0352b-6f51-19e8-a5a8-30cc70420a70}"
    }
  }
}