I've hit two crashes on slack this morning just trying to interact with slack's primary UI. This bug was filed from the Socorro interface and is report bp-4c9d5674-9bbb-41c1-8f15-46c7d0180222. The other crash was bp-8bf4a96c-c7a6-41dd-b675-205e20180222. I'm reasonably confident this wasn't in last night's nightly, so I'd identify the regression window as https://hg.mozilla.org/mozilla-central/pushloghtml?fromchange=994a684a7564c2735d98d6910a78d079a68f0b25&tochange=ea3da643422c58d65335f1778dd6c89c09911585 ============================================================= Top 10 frames of crashing thread: 0 libxul.so void mozilla::ContainerState::FinishPaintedLayerData<mozilla::PaintedLayerDataNode::PopPaintedLayerData [clone .cold.839] 1 libxul.so mozilla::PaintedLayerDataNode::PopPaintedLayerData 2 libxul.so mozilla::PaintedLayerDataNode::Finish layout/painting/FrameLayerBuilder.cpp:2877 3 libxul.so mozilla::PaintedLayerDataNode::FinishAllChildren 4 libxul.so mozilla::PaintedLayerDataNode::Finish layout/painting/FrameLayerBuilder.cpp:2829 5 libxul.so mozilla::PaintedLayerDataNode::FinishAllChildren 6 libxul.so mozilla::PaintedLayerDataNode::Finish layout/painting/FrameLayerBuilder.cpp:2829 7 libxul.so mozilla::ContainerState::Finish 8 libxul.so mozilla::FrameLayerBuilder::BuildContainerLayerFor 9 libxul.so nsDisplayTransform::BuildLayer =============================================================