  This work presents a systematic study of navigational tracking, the latest
development in the cat-and-mouse game between browsers and online trackers.
Navigational tracking allows trackers to 'aggregate users' activities and
behaviors across sites by modifying their navigation requests. This technique
is particularly important because it circumvents the increasing efforts by
browsers to partition or block third-party storage, which was previously
necessary for most cross-website tracking. While previous work has studied
specific navigational tracking techniques (i.e. "bounce tracking"), our work is
the first effort to systematically study and measure the entire category of
navigational tracking techniques. We describe and measure the frequency of two
different navigational tracking techniques on the Web, and find that
navigational tracking is present on slightly more than ten percent of all
navigations that we made. Our contributions include identifying 214 domains
belonging to at least 104 organizations tracking users across sites through
link decoration techniques using direct or indirect navigation flows. We
identify a further 23 domains belonging to at least 16 organizations tracking
users through bounce tracking (i.e. bouncing users through unrelated third
parties to generate user profiles). We also improve on prior techniques for
differenting user identifiers from non-sensitive information, which is
necessary to detect one class of navigational tracking. We discuss how our
findings can used to protect users from navigational tracking, and commit to
releasing both our complete dataset and our measurement pipeline
