[tor-bugs] #28372 [Applications/Tor Browser]: determine if onvisibilitychange is a fingerprinting vector

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#28372: determine if onvisibilitychange is a fingerprinting vector
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 Reporter:  mcs                          |          Owner:  tbb-team
     Type:  defect                       |         Status:  new
 Priority:  Medium                       |      Milestone:
Component:  Applications/Tor Browser     |        Version:
 Severity:  Normal                       |     Resolution:
 Keywords:  tbb-fingerprinting,ff60-esr  |  Actual Points:
Parent ID:                               |         Points:
 Reviewer:                               |        Sponsor:
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Comment (by tom):

 Probably best to disable it... It's not a super important API, should
 degrade just fine. A website could determine:

 - If it was loaded as a prerender client hint (although we probably also
 disable that)
 - If the user has backgrounded the tab, minimized the window, their
 screensaver has gone off, screen locked, etc.

 There's not a lot to learn from these which might be an argument to leave
 it alone, but if I wanted to put on my really creative hat, maybe a
 website could learn that a user's screensaver turns on after X minutes of
 inactivity?

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/28372#comment:1>
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