On my linux firefox box this works perfectly. all I wanted was a button to click to modify my proxy to the already running Tor connection I have (systemd tor service), and it does just that. As already stated, you need a tor connection established, and enable this extension access to private windows.

does what it says on the tin. Thanks
Edit: 1 request, an option to have the icon just say TOR, much like the FF "VPN" button.