Assure pano thumbnail to be embedded at full Facebook timeline/newsfeed width.
I think it was somewhere in 2015 that Facebook changed its options for embedding a thumbnail/preview in a timeline/newsfeed, making it possible to have images at full width with a text below. Of course this is key for attracting eyeballs and viewer clicks.
I will email screenshots for reference with the same title.
Now Facebook shows a preview mode of the panoramas.