Browsers sometimes returning "Server not found" even with firewall disabled

Hi there!
I recently installed NixOs on my main machine and everything is going slowly into place. One problem that I could not solve by any means is this: after a fresh install, both installed browsers (firefox and chromium) sometimes return a “Server Not Found” error. These failures don’t seem to have a pattern, sometimes I can connect to a page and after reloading the page returns an error.

I have a stable connection, and the wifi is connecting properly (git, ping and curl never had problems), so I don’t think that is the cause of the problem.

I’ve tried to disable the firewall, but it seems to have no effect.

As of my system, I am running a laptop with the gnome desktop manager and gdm. I mostly left untouched the configs related to networking.