Rated 5 out of 5 stars

You don't need to install any extension to setup a proxy. On thunderbird 2, you can click on tools, options, advanced, general tab, then click on the config button. Then you change the settings you need. There are more instructions on which settings to change on this page (http://kb.mozillazine.org/RSS_proxy_(Thunderbird))

This review is for a previous version of the add-on (1.4).