Examine source code of Email Tracker for Firefox

{
  "manifest_version": 3,
  "name": "Email Tracker for Firefox",
  "version": "1.0",
  "description": "Tracks if your emails are opened by injecting a tracking pixel.",
  "permissions": [
    "storage",
    "activeTab",
    "scripting"
  ],
  "host_permissions": [
    "https://mail.google.com/*"
  ],
  "content_scripts": [
    {
      "matches": [
        "https://mail.google.com/*"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_end"
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "mail-tracker@kk.com",
      "strict_min_version": "58.0"
    }
  }
}