window.name provides a simple cross-origin tracking method of the same tab:

window.name = "8pdRoEaQCpsjtC8w07dOy7xwXjXrHDyxxmPWBUxQKrh7xfJ4SYFH8QClp6U9T+Ypa8IEa5AwFw3x"

Go to completely different web site and window.name stays the same.

See also: https://2019.www.torproject.org/projects/torbrowser/design/ provides a library build on top of window.name: https://www.thomasfrank.se/sessionvars.html.

See also: https://html.spec.whatwg.org/#history-traversal; this feature should not be ncessary for Firefox 86 or newer https://bugzilla.mozilla.org/show_bug.cgi?id=444222.