I am using Premium ... My inbox will correctly receive emails with the alias, but when I reply, my response gets forwarded back to me. It won't go to the original sender even though their email is in the To field. Very frustrating. I tested with SimpleLogin and everything works fine. I tested with Skiff alias and everything worked fine. Definitely an issue with Firefox and it's not worth the time to investigate and troubleshoot when the other products work first time.