Very useful add-on for using multiple proxies for different sites. The plugin chooses the right proxy by configuration templates. Very useful and easy to fill. If you want to temporary enable a specific server, it is easy to do from the toolbar button.
One of the disadvantages: you can't use proxy import together with configuration synchronization. If you want to import proxy select templates, you need to disable syncing, because otherwise all imported templates will be erased within the next minute.

Уважаемые разработчики! Обратите внимание на ошибку в слове "откОючить" (Использовать настройки Firefox). Понимаю, мелочь, но каждый раз режет глаза, когда включаю расширение.

Totally useless! Tried to set a proxy for the arch linux forum only (bbs.archlinux.org) and it didn't work.