If you are using Firefox (which popularized this feature) or any modern browser with strict security settings, you’ve likely hit this wall. In this post, we’ll break down why this happens, where the request is actually going, and three concrete ways to fix it without turning off security entirely. The error message is actually very literal. Your browser attempted to fetch a resource (an image, a script, an API endpoint, or a page navigation) using the standard http:// protocol. However, the browser’s internal HTTPS-Only Mode is active, and it is refusing to downgrade to unencrypted HTTP.
Audit your code for stray http:// references today—your users’ browsers are already doing the same. If you are using Firefox (which popularized this
https://yourapp.com/api/proxy ➔ Your Server (Node.js/NGINX): http://legacy-vendor.com/data ➔ Back to Browser. Your browser attempted to fetch a resource (an
HTTPS-Only mode forces the browser to automatically upgrade every request to HTTPS. If the upgrade fails (or if you explicitly hardcode http:// ), the browser throws an error instead of falling back to unsafe HTTP. You cannot fix this by telling your users to turn off HTTPS-Only mode. Instead, you need to fix your code or infrastructure. Fix 1: Use Protocol-Relative or Absolute HTTPS URLs (The Easiest) Never hardcode http:// or https:// in your frontend code. Use protocol-relative URLs (starting with // ) or absolute paths. https://yourapp
April 14, 2026 | Reading Time: 4 minutes