It sounds like an issue with DNS-over-HTTPS. https://support.mozilla.org/en-US/kb/firefox-dns-over-https Changing the DNS in the network settings of the operating system would not fix that.
It sounds like an issue with DNS-over-HTTPS. https://support.mozilla.org/en-US/kb/firefox-dns-over-https Changing the DNS in the network settings of the operating system would not fix that.