This bug was filed from the Socorro interface and is report bp-b54ad2db-c5b9-4284-8dd0-4ad220180624. ============================================================= MOZ_CRASH Reason: MOZ_RELEASE_ASSERT(false) (Duplicate display item!) Top 10 frames of crashing thread: 0 xul.dll AssertUniqueItem layout/painting/nsDisplayList.cpp:141 1 xul.dll nsDisplayListBuilder::BuildCompositorHitTestInfoIfNeeded layout/painting/nsDisplayList.cpp:2261 2 xul.dll nsIFrame::BuildDisplayListForChild layout/generic/nsFrame.cpp:3544 3 xul.dll mozilla::ViewportFrame::BuildDisplayList layout/generic/ViewportFrame.cpp:66 4 xul.dll nsIFrame::BuildDisplayListForStackingContext layout/generic/nsFrame.cpp:3071 5 xul.dll nsLayoutUtils::PaintFrame layout/base/nsLayoutUtils.cpp:3713 6 xul.dll mozilla::PresShell::Paint layout/base/PresShell.cpp:6314 7 xul.dll mozilla::dom::TabChild::RecvRenderLayers dom/ipc/TabChild.cpp:2674 8 xul.dll mozilla::dom::TabChild::PaintWhileInterruptingJS dom/ipc/TabChild.cpp:3476 9 xul.dll static void `anonymous namespace'::HangMonitorChild::InterruptCallback dom/ipc/ProcessHangMonitor.cpp:351 =============================================================

the diagnostic assertion was added in bug 1459997

Fairly low volume on beta 64 and nightly 65, and this signature isn't showing up on 63 release. There are more crashes in nightly than on beta, which makes me think this is related to a nightly-only feature.

Low volume crash, has a priority set. Marking fix-optional to remove this from regression triage. Happy to still take a patch in nightly.