I have added the following line to my /etc/hosts file on Ubuntu:
192.168.0.104 www.tondering.dk www.xzutsfsdet.com
192.168.0.104 is an IP address on my LAN.
www.tondering.dk is a server that exists on the internet.
www.xzutsfsdet.com is a server that does not exist on the internet.
So it seems to me that Firefox only uses /etc/hosts if an external lookup fails, whereas other programs use /etc/hosts before performing an external lookup.
Is there any way to make Firefox behave as the other programs?
My operating system is Ubuntu 20.04 LTS, and my Firefox is version 78.0.2.