It may not work for you, but it's still working for others (like me). I explain this in detail in my post: https://www.facebook.com/theoldlayout/posts/167793385055475 and also in the message that appears when the extension tries to switch.

It does work. It just might not switch your account, which is NOT under the control of this extension, as stated in the explanations. The extension works, it's Facebook that is failing you.