How to Fix Cloudflare 521 Error with Firewall Settings - Fix Firefox Secure Connection Failed for Every Website-Chrome Sync Error: Sign In Again – Troubleshooting Guide

Updated 2026-07-28 06:16:52developer-tools
How to Fix Cloudflare 521 Error with Firewall Settings - Fix Firefox Secure Connection Failed for Every Website-Chrome Sync Error: Sign In Again – Troubleshooting Guide
Before changing system settings, save your work and note the exact error text so you can compare results after each step.

Extra verification checklist

  • Restart the affected app after changing permissions or configuration files.
  • Test the same workflow in a clean browser profile or a temporary user account.
  • Compare the result on another network if the error may be connection related.