1 files changed, 7 insertions, 1 deletions
diff --git a/layout/tables/nsTableColGroupFrame.cpp b/layout/tables/nsTableColGroupFrame.cpp
index 732783428..be5b71bb2 100644
--- a/layout/tables/nsTableColGroupFrame.cpp
+++ b/layout/tables/nsTableColGroupFrame.cpp
@@ -387,7 +387,13 @@ void
 nsTableColGroupFrame::BuildDisplayList(nsDisplayListBuilder*   aBuilder,
                                        const nsDisplayListSet& aLists)
 {
-  nsTableFrame::DisplayGenericTablePart(aBuilder, this, aLists);
+  // Per https://drafts.csswg.org/css-tables-3/#global-style-overrides:
+  // "All css properties of table-column and table-column-group boxes are
+  // ignored, except when explicitly specified by this specification."
+  // CSS outlines and box-shadows fall into this category, so we skip them
+  // on these boxes.
+
+  MOZ_ASSERT_UNREACHABLE("Colgroups don't paint themselves");
 }
 
 nsTableColFrame * nsTableColGroupFrame::GetFirstColumn()