[tbb-bugs] #22788 [Applications/Tor Browser]: Tor Browser rendering hangs when downloading large PDFs

[Tor Bug Tracker & Wiki]

#22788: Tor Browser rendering hangs when downloading large PDFs
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     Reporter:  teor                      |      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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 When downloading a large PDF, such as
 https://www.alchemistowl.org/pocorgtfo/pocorgtfo08.pdf , other tabs failed
 to render, open, or close correctly.

 In particular:
 * tabs would be slow to load,
 * the visible area would be rendered, but scrolling outside the visible
 area would show white space,
 * reloads of Google Docs when activating JavaScript using NoScript opened
 new tabs, rather than reloading existing tabs, and
 * closing tabs by clicking the x in the tab header would sometimes work
 particularly if I held the trackpad down for a while. But a quick click
 would often fail to close tabs.

 I think this is new behaviour in Tor Browser 7.0.1 in high security mode
 on macOS 10.12.5. (I have done similar things in the 6.0 series, and it
 was ok.)

 This is reproducible in high security mode. The only issues reproducible
 in low security mode are:
 * tabs would be slow to load,
 which I believe to be an expected behabviour when downloading a large file
 over the same guard connection.

 It does not happen in Firefox 54.0.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/22788>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
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