If you disable Flash on Microsoft Edge, Microsoft ignores your setting — but only for Facebook’s domains. It sounds too conspiratorial to be true, but a number of generally reliable websites confirm it.
Bleeping Computer: “Microsoft’s Edge web browser comes with a hidden whitelist file designed to allow Facebook to circumvent the built-in click-to-play security policy to autorun Flash content without having to ask for user consent.”
ZDNet: “Microsoft’s Edge browser contains a secret whitelist that lets Facebook run Adobe Flash code behind users’ backs. The whitelist allows Facebook Flash content to bypass Edge security features such as the click-to-play policy that normally prevents websites from running Flash code without user approval beforehand.”