[tbb-bugs] #22788 [Applications/Tor Browser]: Tor Browser rendering hangs when downloading large PDFs on higher security slider levels (was: Tor Browser rendering hangs when downloading large PDFs)

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#22788: Tor Browser rendering hangs when downloading large PDFs on higher security
slider levels
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 Reporter:  teor                      |          Owner:  tbb-team
     Type:  defect                    |         Status:  new
 Priority:  Medium                    |      Milestone:
Component:  Applications/Tor Browser  |        Version:
 Severity:  Normal                    |     Resolution:
 Keywords:  tbb-security-slider       |  Actual Points:
Parent ID:                            |         Points:
 Reviewer:                            |        Sponsor:
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Changes (by gk):

 * keywords:   => tbb-security-slider


Comment:

 Replying to [comment:2 teor]:
 > Replying to [comment:1 cypherpunks]:
 > > Isn't this expected since JIT is disabled in those higher security
 settings? Or should there be a whitelist for anything `pdf.js` (at least
 for the Medium security setting)?
 >
 > No, this seems to happen to *other* tabs only while the PDF is
 downloading, and not once it's loaded. I don't see why other tabs should
 be affected in 7.0.1 / multiprocess at all. But it seems worse than the
 6.0 series, not better.

 I think the cypherpunk is right in pointing to the JIT prefs. The PDF is
 not just download but the rendering is already starting once chunks of the
 pdf are available. And other tabs should be affected as the PDF viewer is
 basically blocking the web content process and in ESR 52 there are only
 two processes a chrome and a content one (e10s multi is not available in
 that series). And it is much worse than in the 6.x series because we had a
 bug in that which did not disable JIT despite what it claimed (see
 #21865).

 I guess we could think about exempting the PDF viewer from the JIT
 restrictions.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/22788#comment:5>
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