Multiproxy Switch is a Firefox add-on that lets you switch between multiple proxy configurations, and it's easy to manage.
It supports to add HTTP, FTP, SSL, SOCKS proxies, also auto proxy configuration.
When you switch the proxy, you can select to clear the cookie to protect privacy, and also reload the page at the same time.
Now Multiproxy Switch supports following languages:
Czech (cs-CZ), German (de-DE), English (en-US), Spanish (es-ES), Persian (fa-IR), French (fr-FR), Hungarian (hu-HU), Icelandic (is-IS), Italian (it-IT), Japanese (ja-JP), Chinese (zh-CN, zh-TW)
As not all of them have been verified, please contact me if you have problem using it.
Thank you all for your great support(language translation).