Is there a way to stop inline video clips from playing on MacOS Safari?
Found on Apple Communities : Stop auto play HTML5 in Safari?


  Open Terminal and enter this command:
  defaults write com.apple.Safari IncludeInternalDebugMenu 1  
  
  That will unhide Safari's "Debug" menu.  Under that menu, go to Media
  Flags, and then select Disallow Inline Video.   This will stop videos
  from automatically playing when a page loads.


Just tested on Facebook - works.