I made another post today and I was even more disappointed than I expected as not only did FB not grab my featured image from Duotone for the thumbnail, they didn't even grab my new avatar that I made three days ago. They actually used the old one! I had posted and saved a new gravatar because I thought if they won't use the featured image, at least I'll have a nice gravatar with the name of my blog. Out of complete and utter frustration for this totally random degradation of my previously perfect system, I just checked the "remove thumbnail" box when I shared with FB. Of course without the thumbnail, only about 10% of my FB friends will find my WordPress blog. Somebody at WordPress needs to call somebody at FB and get this fixed. All you have to do is Google the problem and see the tons of people with the same problem.
I do appreciate everything you've tried to do "Time Thief" as solved every other problem I've ever had. Merry Christmas!