I'm often reading FF and MEF at the same time.  I find that now when I switch between one tab and the other, the messages I've read are gone when I switch back, even if I want to go back and reply to a message I've already read.  This is going to take some getting used to!  Oh, I know how to get to a message again, that's not an issue, it is just a major change not seeing a set block of messages from start to finish!  If it shocks me a bit, I am going to expect to hear from members.  This is NOT a complaint--the new way of keeping track of messages is great--it's just a wow, and I have to adjust after all these many years!