'Incorrect or missing confirmation code'

When I go to log in to my account I get this error message - the confirmation code is definitely correct and so is the password.

I’ve noticed that this only happens in firefox as well. It happens after you’ve added something to your cart and have gone through to the checkout and tried to login there.

Do you know what could be causing this?

ETA: sorry, I’ve just realised that it’s also happening when you try to login from the homepage “sign in” area too, but again, only in Firefox

I can confirm this error too, but i dont know where it comes from.