As with ad blockers, the proportion of "savvy" web users is so small as to effectively not exist. It would be trivial for someone to write a Firefox plugin so

As with ad blockers, the proportion of "savvy" web users is so small as to effectively not exist. It would be trivial for someone to write a Firefox plugin so that every page request on a "protected" domain is given a Google referrer (e.g. https://addons.mozilla.org/en-US/firefox/addon/953 https://addons.mozilla.org/en-US/firefox/addon/953). But unless someone builds this functionality by default into a browser with significant market share, it won't be worth it for the content provider to try to stop.