Same problem as you, Tashgw. So, if you find a solution ...
I take this opportunity to say that I'm quite dissatisfied with the attitude of Avast. Not because I expect them to answer, but, at least, to let the world know my frustration.
When I wanted to renew my EP licence, I had to migrate to AP, that offers much less than EP. No possibility to fill in other forms, no other fields userID and passwords. Few days later, EP wakes up and invites me to renew the licence. A bit surprised, I followed the procedure and obtained a new key for EP. As I don't like AP, I accepted to pay for this new EP key.
So, I paid twice. I sent a message to Avast, but never received aby answer.
Today, I installed a new update for Firefox (48.0), and the EP module is now disabled. No way to obtain a new certificate for EP from Avast.
I hope that Avast will consider that, since I paid for 1 year, they will have to maintain the product for at least one year, and that they will publish a new certificate for FF.
Else I will run Avast products (Internet Sec, Cleanup, EP/AP) untill licences expire, then I'll migrate to other logo's, who provide a real support.