The ‘server is not found’ error is one of the most common issues of the Mozilla Firefox users. This issue can be irritating at a time, that is why you should follow the steps given below to fix the issue at hand:
You need to change the DND to Google’s Public DNS.
Try to do the TCP/IP reset.
You can disable the VPN and proxy server.
Starting the DNS Client service may resolve the error.
Resetting the router can be beneficial for you.
You can even disable the firewall of your system.
If the error persists then you can call Mozilla Firefox technical support
to speak with the experts who can help you in fixing the server error.
Read More: How to fix Mozilla Firefox update failed error?