Is the error of Firefox Proxy Server giving you hard times? If yes, then it can occur because of many reasons; however, you can resolve this error by following the steps mentioned below:
• You need to force Firefox for using the Auto Detect Proxy Settings
• Add the URL SSL port in the allowed list
• You have to switch to HTTPS proxy
• You must disable the built-in proxy server in Windows 7, 8.1, 10
• Uninstall the VPN Client
If these steps don't help you fix the proxy server error, then it's best to reach out to certified experts by calling Mozilla Firefox Support Number that is available 24*7 around the clock.
Read more: - How to Fix the Firefox Proxy Server Error | How to fix 403 forbidden error in Mozilla Firefox