> (I assume /etc/hosts would work for linux?) No, because both www.reddit.com and old.reddit.com (in fact, *.reddit.com) already map to the same IP address. Th

> (I assume /etc/hosts would work for linux?) No, because both www.reddit.com and old.reddit.com (in fact, *.reddit.com) already map to the same IP address. They are distinguished through the Host HTTP header. The only way to do that mapping would be within the browser (or with a MITM proxy, which I wouldn't recommend).