Quick Proxy от Oliora

Note that to use Quick Proxy, you must allow the extension to run in Private Windows (this is a limitation of Firefox’s security model). You can enable this during installation or later via Tools > Extensions and Themes > Quick Proxy > Details.

It’s recommended to pin the Quick Proxy extension to the toolbar for easy access. You can do this during installation (it happens by default) or from the Extensions toolbar menu.

After installation, set up your alternative proxy configurations on the Quick Proxy preferences page. You can access it via Tools > Extensions and Themes > Quick Proxy > Preferences.