[tor-bugs] #21766 [Applications/Tor Browser]: Tor Browser based on ESR52 with e10s enabled crashed while trying to download a file

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#21766: Tor Browser based on ESR52 with e10s enabled crashed while trying to
download a file
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 Reporter:  gk                                   |          Owner:  mcs
     Type:  defect                               |         Status:
                                                 |  needs_review
 Priority:  Very High                            |      Milestone:
Component:  Applications/Tor Browser             |        Version:
 Severity:  Critical                             |     Resolution:
 Keywords:  ff52-esr, tbb-e10s, tbb-crash,       |  Actual Points:
  TorBrowserTeam201705R, tbb-7.0-must            |
Parent ID:                                       |         Points:
 Reviewer:                                       |        Sponsor:
                                                 |  Sponsor4
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Comment (by arthuredelstein):

 I built and manually tested on Windows (with both large files and very
 small files) and it works! I wasn't able to reproduce the problem seen in
 OSX in comment:36.

 In the patch, I notice there are a few calls in
 `nsExternalAppHandler::OnStartRequest` where you get a return value,
 assign it to `rv` and ignore it. I wonder what should be done if
 `Suspend()` or `ShouldCancel()` or `Resume()` returns an error code? Or
 potentially  the `Unused << Function();` construct could be used instead:
 https://dxr.mozilla.org/mozilla-esr52/source/mfbt/Unused.h

 Otherwise the patch looks good to me.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/21766#comment:37>
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