I use Facebook a lot. I watched a video earlier that someone had posted and all went well. So a little later, when I wanted to show it to my daughter, once again this darn box popped up which since I can't resolve it as my Windows 8.1 apparently comes stock with Flash Player so clicking for a new installation does NOTHING internally.
The Adobe site ran it's check and I saw that little floating cloud that verified that I have Flash Player installed and that it works and is Enabled. I've also researched this NUMEROUS times and found that it's easy to just click the gear in top-right on my IE-11 and Manage Add-Ons then make sure it is Enabled, which it always has been.