[tbb-bugs] #21410 [Applications/Tor Browser]: Pagewise scrolling up with [Shift]+[Space] not working on some websites

[Tor Bug Tracker & Wiki]

#21410: Pagewise scrolling up with [Shift]+[Space] not working on some websites
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     Reporter:  Runawe                    |      Owner:  tbb-team
         Type:  defect                    |     Status:  new
     Priority:  Medium                    |  Milestone:
    Component:  Applications/Tor Browser  |    Version:
     Severity:  Normal                    |   Keywords:
Actual Points:                            |  Parent ID:
       Points:                            |   Reviewer:
      Sponsor:                            |
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 On some websites, like articles on https://www.nytimes.com/, one can
 scroll down pagewise with [Space] key, but not scroll up with
 [Shift]+[Space]. Pressing [Shift]+[Space] results in scrolling down one
 screen page; it should scroll up one screen page.

 This seems to be related to JavaScript. Current Tor Browser 6.5 is
 affected in default settings, meaning security slider on low, but also on
 medium. When security slider is set to high, there is no problem scrolling
 up with [Shift]+[Space]. Also tested in Tails. (As far as I remember, this
 problem was also present in versions before 6.5.)

 Testing in other (non Tor) browsers, [Shift]+[Space] works as expected,
 scrolling up pagewise. Also with uBlock Origin active or NoScript and some
 JavaScript blocked.

 Example article where scrolling up with [Shift]+[Space] does not work in
 Tor Browser with default settings:
 https://www.nytimes.com/2017/02/07/opinion/blaming-america-first.html?_r=0

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/21410>
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