download Facebook videos ?

If you download someone else's video from Facebook, they will not receive a notification, as Facebook does not currently have this feature. However, you need to modify the visuals and certain details if you wish to reuse that video on the same platform.

Not at all. Facebook has never notified users when someone downloads a video, though I imagine they might add this feature in the future.

No, Facebook doesn't send any notifications. But what do you plan to use the downloaded video for?