You can use the same technique with a:active to track link clicks, by the way. Technically, this would all be relatively easy to block with your own user style

You can use the same technique with a:active to track link clicks, by the way. Technically, this would all be relatively easy to block with your own user style sheet. Practically, though, a lot of non-tracking sites rely on background-image for essential functionality, so you'll see a lot of breakage. It's a dilemma.