I've been finding that browsing has been slow for me lately on my linux box, which has Ubuntu 16.04 installed. After some investigation it seemed worthwhile to try to install a DNS cache to speed up DNS queries. This has sped up successive DNS queries from 21ms to 0ms, removing sluggishness.
sudo apt install bind9 cd /etc/resolvconf/resolv.conf.d sudo echo "nameserver 127.0.0.1" >> head
Apply the configuration as follows:
sudo resolvconf -u
The improvement can be seen by using dig to query a domain and looking at the Query time output. After the first dig, subsequent digs return in 0 ms.