No webpage is an island.

Every time you click a link on the internet, you set off a cascading series of events. Some are the ones you would expect: the site needs to talk to a server to download images, for example, which takes some time. Others are less obvious. These are the obscure URLs that flash by at the bottom of your browser, and slow the whole process down.

Those little URLs are just the tip of the iceberg, and Ghostery is a free browser extension that lets you see the whole thing. For example, here’s what Ghostery, which sits in the background while you browse, tells us about those invisible parts of this IMDB page:

To see the IMDB page for Pacific Rim, my browser talked to nearly 30 sites outside of IMDB (disclosure: BuzzFeed racks up about 15, and the NSA’s official website counts just one: Google Analytics).

They’re a mixture of advertising sites, tracking software, analytics tools and social plugins — tweet buttons, Facebook buttons and the like. A lot of the names in the lists will be familiar: Google, Amazon, etc. For the ones that aren’t, Ghostery gives you a summary of what they do. Usually the weirder ones are ad products; sometimes, they’re pleasant surprises:

The Most Important Piece Of Software You’ve Never Heard Of

One of the first things I install on a browser.