When browsing with Firefox, I use Privoxy as a proxy to avoid annoying popups and other intrusive advertising. However, there are some sites where privoxy interferes with the correct operation of the site, and it was a pain to have to drill down through Firefox’s menus to turn off the proxy.
SwitchProxy is an extension for Mozilla and Firefox that puts an additional toolbar on the browser so that one can switch between proxies or have no proxies at all. It also allows one to use a proxy that works as an anonymizer while browsing.