What Is Facebook Up To?

I have a widget/app installed on my computer, juno, that allows me to monitor, at a glance, the CPU, network, and disk activity, among other items, including the phase of the moon. (It is called gkrellm, and is delivered as part of the Ubuntu Linux distribution.)

Recently I noticed some odd behavior that I tracked down to Facebook.  When I'm logged into Facebook, my computer has constant network (Internet) activity varying between 12 and 24 Kbytes/sec. This caught my eye, because my network is normally quiescent and sporadic except when refreshing a browser page, or downloading, or when I'm sent an email with a large attachment. When I log out of Facebook, the traffic immediately plummets:

The charts make it appear that there are roughly equal amounts of reading from and writing to the Internet. This makes me wonder what Facebook is doing that I'm not aware of: no other web site (I usually have 7 or 8 tabs up) shows this behavior. Is it just sloppy Facebook programming? Why should it be running all the time?

I've now adopted the habit of logging into Facebook, checking for updates, and logging out again. The drain on the computer from Facebook is small, but it offends my programmer's sensibility. This practice also reduces on-line distraction, which is a good thing.