Rated 4 out of 5 stars
1. It slows down Internet
2. It is impossible to remove this addon. As soon as it is removed, every time on restart or launching Firefox the autorization window requires my username and password and It is impossible to prevent this through Menu->Tools->FasTun Options, because the FasTun is removed.
You should find the solution for this case - it is not applicable, that it is impossible to remove addon!
3. Sorry, it is possible to remove this addon without autorization window suffering:
Firefox Options -> Advanced -> Net -> Options -> Without proxy.
(Настройки ФайрФокса -> Дополнительные -> Сеть -> Настроить -> без прокси)