If you are just searching for http proxy you can try privoxy or polipo and if you are seaching for anonimity on the web you can try tor. Tor used to have torbutton plugin for firefox but seems they give their own browser. What I recommend is search for an addon to switch proxies in firefox. So what you can do is install tor.

sudo apt-get install tor

and configure polipo to work with tor:

cd /etc/polipo/

sudo wget https://gitweb.torproject.org/torbrowser.git/blob_plain/HEAD:/build-scripts/config/polipo.conf -O config

If you use chrome/chromium you can setup torbutton like setup through this

If you just want one-time proxy just install polipo or privoxy [BUT NOT BOTH]

Go to firefox > preference > advanced > network and setup manual proxy with

ip: localhost

port: 8118