Examine source code of Reading Time Estimator v2

{
  "manifest_version": 2,
  "name": "Reading Time Estimator",
  "version": "1.0",
  "description": "Estimate the reading time for the text on your current webpage.",
  "permissions": [
    "activeTab"
  ],
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": "icons/icon.png"
  },
  "icons": {
    "48": "icons/icon.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{d5b0ed5e-de82-463c-a9fa-cd5cd812931d}"
    }
  }
}