I use AddThis on my site which includes the Facebook Like button and Twitter button. I also run Adsense.
Every time I run the speed test, these scripts are dramatically slowing down the load time. Each of them takes at least 6 seconds, sometimes over 20!! The DNS/TTFB are fine but the “Content Download” is what’s taking the time.
But I don’t get anywhere close to that when I load pages myself, even on an old computer using IE, with a cleared cache. Why is there such a big delay for WebPageTest?