Thank you for helping me troubleshoot this!
I did, indeed find that the problem was not AVAST or my browsers (Edge, Chrome or Firefox). This afternoon it occurred to me that my ACRONIS program has security tools that I have always deactivated. However, my ACRONIS subscription was just renewed and the program changed. I went into those ACRONIS settings and found that the security feature had been turned on. When I deactivated that tool, I had no problem logging into my Discover accts.
I was perplexed and frustrated but I greatly appreciate the time you took to help me with this. I hope my experience, documented here, can help someone else.
Kristin