It's quite possible to break the Internet by blanket-blocking core Google IPs[1]. I tried blocking these in my firewall and my surfing sessions became really slow. I would much prefer things like uBlock which do it at the browser level and it doesn't cause a lag.

    74.14.192.0/18
    216.58.192.0/19
    216.239.32.0/19
    64.233.160.0/19
    66.249.80.0/20
    72.14.192.0/18
    209.85.128.0/17
    66.102.0.0/20
    74.125.0.0/16
    64.18.0.0/20
    207.126.144.0/20
    173.194.0.0/16 

This is usually because if you're resolving domains to 0.0.0.0 or 127.0.0.1 in hosts then there is an inbuilt timeout as localhost is typically not running any services.

Best to make localhost run a service. A personal thing I use is lighthttpd[2] which ensures such a lag is vanished

[1]: https://gist.github.com/int64ago/1d72c80e8082b78777c9

[2]: https://en.wikipedia.org/wiki/Lighttpd