It's odd. Still get it. Here's the steps I took:
(1) Opened FF and cleared the cache, Closed FF.
(2) Opened NOD32 8, went to Advanced setup.
(3) Set to "Always scan SSL protocol". Checked the two boxes "Apply created exceptions
based on certificates" and "Block ... SSL v2".
(4) Under Certificates I have checked "Add the root certificate to known browsers"
(5) Clicked OK and closed NOD32 GUI.
(6) Opened FF and went to forum.eset.com
(7) Got a popup from ESET (see attached).
(8) If I click on "Yes" I get an error message from FF (not the one shown in my first post).
(9) If I tell FF to Try Again, the same NOD32 dialog pops up.
(10) If I answer "Yes, always" the cert gets added to NOD32's "Trusted Certificates".
But then I get the message from FF that I attached in my opening post.
I suppose I could just click on "Add Exception" in that FF dialog, but it seems strange
that I should have to do that.
FWIW on another system here with Bitdefender IS 2015 and SSL scanning enabled, I don't
get that FF message from these forums.