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

[Tor Bug Tracker & Wiki]

#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     |    Version:
  Browser                            |   Keywords:  tbb-
     Severity:  Normal               |  fingerprinting,ff60-esr
Actual Points:                       |  Parent ID:
       Points:                       |   Reviewer:
      Sponsor:                       |
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 In Firefox 56, Mozilla added support for onvisibilitychange. See:
 https://developer.mozilla.org/en-
 US/docs/Web/API/Document/onvisibilitychange
 https://bugzilla.mozilla.org/show_bug.cgi?id=1333912

 We should think about whether this introduces any new fingerprinting
 risks. The following mentions a prerender state which we (mcs and brade)
 do not fully understand:
 https://w3c.github.io/page-visibility/#privacy-security

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/28372>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
The Tor Project: anonymity online