[tbb-bugs] #31954 [Applications/Tor Browser]: Make sure -webkit-device-pixel-ratio is no fingerprinting risk

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#31954: Make sure -webkit-device-pixel-ratio is no fingerprinting risk
-------------------------------------------------+-------------------------
 Reporter:  gk                                   |          Owner:  tbb-
                                                 |  team
     Type:  task                                 |         Status:  closed
 Priority:  Medium                               |      Milestone:
Component:  Applications/Tor Browser             |        Version:
 Severity:  Normal                               |     Resolution:  fixed
 Keywords:  tbb-fingerprinting-resolution,       |  Actual Points:  0.1
  ff68-esr, TorBrowserTeam201910                 |
Parent ID:                                       |         Points:  0.25
 Reviewer:                                       |        Sponsor:
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Changes (by gk):

 * keywords:  tbb-fingerprinting, ff68-esr, TorBrowserTeam201910 => tbb-
     fingerprinting-resolution, ff68-esr, TorBrowserTeam201910
 * status:  new => closed
 * resolution:   => fixed
 * actualpoints:   => 0.1


Comment:

 The Mozilla ticket actually flips just a pref. The implementation work got
 done back in https://bugzilla.mozilla.org/show_bug.cgi?id=1176968. One can
 see from the test at https://hg.mozilla.org/mozilla-
 central/rev/48f644f1c41e that the webkit version is essentially an alias
 for the moz version (as the [https://developer.mozilla.org/en-
 US/docs/Web/CSS/@media/-webkit-device-pixel-ratio implementation notes in
 the Browser compatibility table for Firefox] say).
 `GetScreenPixelsPerCSSPixel()` calls `GetDevicePixelRatio()` and that in
 turn `GetDevicePixelRatioOuter()` which is taking care of our
 fingerprinting concerns (https://searchfox.org/mozilla-
 esr68/source/dom/base/nsGlobalWindowOuter.cpp#3685). So, we are good here.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/31954#comment:1>
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