THIS one is no longer available.
Overlay Blocker is no longer available in the Chrome store, but they now have one called BehindTheOverlay. BehindTheOverlay Chrome Extension Kills Overlay Popups. It works, so far.
Here is the one for Firefox:
It may need to be tweaked one some social media websites, so just play around with it and perhaps whitelist some sites, if they don't offer full functionality. At least this should stop alot of that nonsense.