--- a/layout/base/nsCSSFrameConstructor.cpp
+++ b/layout/base/nsCSSFrameConstructor.cpp
@@ -3284,18 +3284,17 @@ nsCSSFrameConstructor::ConstructFieldSet
           NS_NewColumnSetFrame(mPresShell, fieldsetContentStyle, nsFrameState(0));
         InitAndRestoreFrame(aState, content, parent, columnSetFrame);
         innerSC = mPresShell->StyleSet()->ResolveAnonymousBoxStyle(
                     nsCSSAnonBoxes::columnContent, fieldsetContentStyle);
         if (absPosContainer) {
           absPosContainer = columnSetFrame;
         }
       }
-      contentFrame = NS_NewBlockFrame(mPresShell, innerSC,
-                                      NS_BLOCK_FLOAT_MGR | NS_BLOCK_MARGIN_ROOT);
+      contentFrame = NS_NewBlockFormattingContext(mPresShell, innerSC);
       if (columnSetFrame) {
         InitAndRestoreFrame(aState, content, columnSetFrame, contentFrame);
         SetInitialSingleChild(columnSetFrame, contentFrame);
         contentFrameTop = columnSetFrame;
       } else {
         InitAndRestoreFrame(aState, content, parent, contentFrame);
         contentFrameTop = contentFrame;
       }