Examine source code of D3Metrics

{
  "manifest_version": 2,
  "name": "D3Metrics",
  "version": "1.1",
  "author": "David Haynes",
  "description": "Checks a website for Google Tag Manager, Google Analytics and Facebook Pixel. If found, it will display the account ID for each platform.",
  "homepage_url": "https://git.d3corp.com/d3-metrics/firefox-extension",
  "icons": {
    "48": "icons/bar-chart-48.png"
  },
  "permissions": [
    "activeTab",
    "tabs",
    "clipboardWrite"
  ],
  "browser_action": {
    "browser_style": true,
    "default_icon": "icons/bar-chart-32.png",
    "theme_icons": [
      {
        "light": "icons/bar-chart-32.png",
        "dark": "icons/bar-chart-32.png",
        "size": 32
      }
    ],
    "default_title": "D3Metrics",
    "default_popup": "popup/gtm.html"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{26e9e9ed-0e8c-4e5e-bc56-0b7614c5eeb8}"
    }
  }
}