Examine source code of Performance Heatmap

{
  "manifest_version": 2,
  "name": "PH",
  "version": "1.0",
  "description": "Marks elements on the page based on their performance metrics.",
  "permissions": [
    "activeTab"
  ],
  "browser_action": {
    "default_popup": "popup.html"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{92bc49fb-e9de-4ca2-aeb2-7ee46068c70b}"
    }
  }
}