It's hard to get a clear picture of what sites your browser is communicating with as you traverse the myriad destinations provided by the internet. Sure, it's obvious what website you're looking at, but what other connections are being made in the background? Now Firefox users can see a visualisation of this information using a Mozilla-developed add-on called Lightbeam.
Previously called Collusion, the add-on's received a bit of a facelift and a subsequent rebranding, but the core functionality is relatively unchanged.
Depending on how you have Firefox configured, activating Lightbeam once installed could prove extremely mysterious. After hunting around the UI trying to track down an icon to click or menu option to select, a thread on Mozilla's support forum revealed that you have to hit Alt to bring up the menu bar, from which you can turn on Lightbeam by going to Tools > Show Lightbeam.
With the Lightbeam tab open, you can begin navigating the web and with each site you visit, new nodes will appear in Lightbeam's Graph view. The main nodes will have child nodes showing you the other sites being interacted with, giving you a neat visualisation of exactly what's going on in the background. You can also check out the Clock and List views, but they're nowhere near as useful, at least not immediately.
It's still being tweaked by Mozilla -- I noticed that performance isn't that great while the Graph view is populating, but is fine once it's finished updating. Otherwise, it does what it says on the tin and it'll be interesting to see what additional features Mozilla adds as development continues.