This. I use the no script addon by default, and it’s amazing how many different domains sites try to bring in. Then I hit Twitter, imgurl, quora, etc and I am left with nothing but a blank page with plain text telling me that I need JavaScript to view the site. It makes me wonder what kind of tracking they are pushing.
All of them. If you allow everything and have Ghostery running in "don't block anything but tell me what's there" mode, it's horrifying just how many things get loaded.
You can play with page load sizes in the debugger console with stuff blocked and without too - about half the downloaded material on any major news website is stuff that Ghostery will block. It's quite terrifying.