Privoxy (https://www.privoxy.org/):

> Privoxy is a non-caching web proxy with advanced filtering capabilities for enhancing privacy, modifying web page data and HTTP headers, controlling access, and removing ads and other obnoxious Internet junk. Privoxy has a flexible configuration and can be customized to suit individual needs and tastes. It has application for both stand-alone systems and multi-user networks.

> Privoxy is Free Software and licensed under the GNU GPLv2.

I'm from Bangladesh, my connection is ~256 kbps and my pc is slow (256 RAM and 1.6 ghz), if not by privoxy, i couldn't browse internet.

Squid can do this easily. Just setup an acl that blocks requests for file extensions you don't want.

  acl Blocked_extensions urlpath_regex -i "/etc/squid3/blocked.extensions.acl"
  http_access deny Blocked_extensions

The contents of /etc/squid3/blocked.extensions.acl would be something like:

  \.css$
  \.css\?.*$
  \.js$
  \.js\?.*$
  \.woff$
  \.woff\?.*$
  \.eot$
  \.eot\?.*$
  \.svg$
  \.svg\?.*$

It's also easy to run squid in transparent proxy mode if you want to support older devices that don't let you manually specify a proxy.