try this,

In the address bar, type about:config and press enter and accept the warning, search for network.dns.disableIPv6 and double-click to set its value

It was already disabled but I enabled it and same issue so I disabled it again. Still same issue.

go to options > general > network > settings

and choose Auto-detect proxy settings for this network

Tried that also. Didn't make a difference. Still receive the server not found error.

Some additional information...

When I ping www.google.com, www.firefox.com and others I receive a cannot find host or server message.

NoGMO said

Some additional information... When I ping www.google.com, www.firefox.com and others I receive a cannot find host or server message.

That to me would indicate ISP problems.

Try this:

TCP/IP stack repair options for use with Windows XP with SP2 or SP3.

Start, Run, CMD, OK to open a command prompt.

Reset WINSOCK entries to installation defaults: netsh winsock reset catalog

Reset TCP/IP stack to installation defaults. netsh int ip reset reset.log

Reboot the machine.

Thanks, but not a Windows box.

The wireless connection is being made. I just verified with the my isp.

It seems to be something in netplan. I created a 01-netcfg.yaml in /etc/netplan and added

nameservers:

        addresses: [8.8.8.8, 8.8.4.4]

Rebooted the box and still am having difficulties with urls.

Any ideas?

see the answer here:

• https://askubuntu.com/questions/1021884/no-internet-after-upgrade-from-16-04-to-18-04