[tor-bugs] #16983 [Tor Browser]: Favicon requests not isolated if one opens the tab list dropdown

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#16983: Favicon requests not isolated if one opens the tab list dropdown
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     Reporter:           |      Owner:  tbb-team
  someone_else           |     Status:  needs_review
         Type:  defect   |  Milestone:
     Priority:  major    |    Version:
    Component:  Tor      |   Keywords:  tbb-linkability,
  Browser                |  TorBrowserTeam201509R
   Resolution:           |  Parent ID:
Actual Points:           |
       Points:           |
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Comment (by arthuredelstein):

 To clarify further: the point of the demo is to try to answer Georg's
 question in comment:7.

 But under normal usage, we wouldn't be using a "popupshown" listener to
 modify the `image` attribute. Instead, the `image` attribute is copied
 from the `tab` to the `menuitem`. The menuitem should normally cause no
 extra image downloads, because the `tab` has already caused the image to
 be added to the cache, isolated to the appropriate first party.

 Absent this patch, the `menuitem` does not find the image in the cache,
 because it is using -No-First-Party-. So it downloads the image again over
 the -No-First-Party- circuit.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/16983#comment:12>
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