[tbb-bugs] #30542 [Applications/Tor Browser]: pinch-to-zoom viewport vs other screen/window

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#30542: pinch-to-zoom viewport vs other screen/window
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 Reporter:  Thorin              |          Owner:  tbb-team
     Type:  defect              |         Status:  new
 Priority:  Medium              |      Component:  Applications/Tor Browser
  Version:                      |       Severity:  Normal
 Keywords:  tbb-fingerprinting  |  Actual Points:
Parent ID:                      |         Points:
 Reviewer:                      |        Sponsor:
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 I am not sure if this is an issue for TB. I do not have a touch device on
 which to install TB8. But since Tor Uplift's RFP underlines this
 protection, it might be prudent for someone to check it out.

 My Android has a low screen res, the web content loads at a higher res -
 when I pinch to zoom and re-run/refresh: the viewport shows entropy.
 Ignore the css media measurements. Just focus on the five JS results:
 screen, available screen, outer, inner and viewport

 Control
 - device should be hidpi/retina/whatever-you-call-it
 - load test page [1]
 - all the widths/heights (except viewport: e.g 17px less width) should be
 the same (i.e `1000 x 1000`)
 - zoom in to `133%`
 - refresh or rerun button
 - all the widths/heights (except viewport e.g 13px less width) should be
 the same (e.g `750 x 750`)

 STR
 - device should be hidpi
 - load the test page
 - all the widths/heights (except viewport) should be the same (e.g `980 x
 1522`)
 - zoom in (fingers on a touch device)
 - scroll to the left and hit `re-run tests`
 - scroll back to the right and viewport is still based on the old value
 - also, in the pic in [2] css media still shows it's using the old values
 (`980`) (ignore that it's missing the height values: not sure why it does
 that: I think it's because it hits a fraction, I see the same thing on
 desktop)


 Is this just a quirk? Or is the viewport not properly spoofed in all
 situations?

 [1] https://ghacksuserjs.github.io/TorZillaPrint/TorZillaPrint.html#screen
 [2] https://github.com/ghacksuserjs/TorZillaPrint/issues/34

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/30542>
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