How to reply to PM?

I just sent you a test PM (private message). You should see a red number by the envelope. Click that and look for my PM. It should be at the top of the PM list and highlighted. Is the reply box present? If not take a screenshot and post it here.

That's because this part is broken, at least when using FireFox. You have to sign out and in. But your profile menu with the sign out link may be broken too and does not show up. See following topic, there is at least a workaround.