Rated 4 out of 5 stars

Good add-on, but there is an errors when loading the list socks proxy from a file or url

http://50na50.net/GuifiProxyList.csv (free 50 proxy)

This review is for a previous version of the add-on (3.0.3). 

fixed @v3.0.4

https://addons.mozilla.org/en-US/firefox/addon/guifiproxy/versions/?page=1#version-3.0.4