This is strange! - and its been this way for --- what, a looong time!
Enco login session has always had issues with non IE browsers. We've discussed it here many times.
Couple years ago, I just accepted that I would straight off open up an IE page, do my order and not have the hassle.
Hey, with Encos perks (love those perks - free ship, % off, sales), decent products, and good service, I can jump thru a hoop or 2
If everything seems to be going well, you have obviously overlooked something........