Google Not Installing Third Party Cookies — It’s Firefox Prefetching

John Battelle spotted a

from Chris Marino at Tumbling Duke that has the worrisome suggestion
that Google is allowing third parties to set cookies based on searches people
do. But I dropped an IM to Dave Naylor,
who immediately spotted this being due to Firefox prefetching.

If you use Firefox, Google will automatically preload the pages showing in
the top search results. They made this
change back
in March. As they warned back then:

With prefetching enabled, you may end up with cookies and web pages in your
web browser’s cache from web sites that you did not click on since prefetching
happens automatically when you view Google search results pages. You can
delete these files by clearing your browser’s cache and cookies.

So in Chris’s case, he writes about how he searched for cars, Amazon and
Walmart and got cookies from, and Walmart. He assumed this
is all related to AdWords in some way.

AdWords isn’t the issue. It’s because for a search on cars, was the
first site listed and so that page was preloaded — and that meant a cookie from came with it. It’s the same situation was true for Amazon and Walmart.
in searches on their names.

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