[tbb-bugs] #22618 [Applications/Tor Browser]: Downloading pdf file via file:/// is stalling if the external helper dialog is enabled

[Tor Bug Tracker & Wiki]

#22618: Downloading pdf file via file:/// is stalling if the external helper dialog
is enabled
-------------------------------------------------+-------------------------
 Reporter:  gk                                   |          Owner:  tbb-
                                                 |  team
     Type:  defect                               |         Status:
                                                 |  needs_review
 Priority:  Medium                               |      Milestone:
Component:  Applications/Tor Browser             |        Version:
 Severity:  Normal                               |     Resolution:
 Keywords:  tbb-7.0-issues, tbb-regression,      |  Actual Points:
  tbb-e10s, TorBrowserTeam201707R                |
Parent ID:                                       |         Points:
 Reviewer:                                       |        Sponsor:
-------------------------------------------------+-------------------------
Changes (by mcs):

 * keywords:  tbb-7.0-issues, tbb-regression, tbb-e10s => tbb-7.0-issues,
     tbb-regression, tbb-e10s, TorBrowserTeam201707R
 * status:  new => needs_review


Comment:

 Kathy and I looked at getting rid of the extra dialog but decided against
 it for three reasons:
 1. The warning we currently display is shown for all downloads and
 external protocol accesses (e.g., mailto: links) and we should preserve
 that behavior. It appears that the preferences discussed in
 https://bugzilla.mozilla.org/show_bug.cgi?id=440892 were only effective
 for external protocols.
 2. It would be difficult to fit meaningful warning text into Mozilla's
 existing protocol and "download or save" prompts.
 3. We have an existing preference (`extensions.torbutton.launch_warning`)
 that we should continue to support.

 Instead, we dove in deeper and added support to the core browser code to
 displaying our existing warning dialog modelessly as is done for Mozilla's
 dialogs. We had to define some new objects and interfaces to make this
 work, but Kathy and I believe this is a much better fix for #21766 (our
 testing confirms that this ticket – #22618 – is fixed as well as #22471,
 #22472, and #22610). What's the downside? A more complex patch to the core
 browser code and somewhat tight linkage between the browser code and part
 of Torbutton. Still, the results are good.

 The following branch contains two patches, one to revert the previous
 patch and one to do things the new way:
 https://gitweb.torproject.org/user/brade/tor-
 browser.git/log/?h=bug21766-04
 Most of the changes are to split up existing code so that interaction with
 the Torbutton component is done asynchronously. We also had to add an
 `nsExternalLoadURIHandler` class to provide a request-specific object to
 hold information about each external protocol request while our download
 warning prompt is displayed.

 Our Torbutton changes are here (one patch):
 https://gitweb.torproject.org/user/brade/torbutton.git/log/?h=bug21766-01
 Note that we reopened #22434 since we now understand what that ticket was
 about.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/22618#comment:7>
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