--- a/layout/generic/nsFlexContainerFrame.cpp
+++ b/layout/generic/nsFlexContainerFrame.cpp
@@ -1197,23 +1197,16 @@ nsFlexContainerFrame::CSSAlignmentForAbs
     alignment = NS_STYLE_ALIGN_START;
   } else if (alignment == NS_STYLE_ALIGN_LAST_BASELINE) {
     alignment = NS_STYLE_ALIGN_END;
   }
 
   return alignment;
 }
 
-bool
-nsFlexContainerFrame::IsHorizontal()
-{
-  const FlexboxAxisTracker axisTracker(this, GetWritingMode());
-  return axisTracker.IsMainAxisHorizontal();
-}
-
 UniquePtr<FlexItem>
 nsFlexContainerFrame::GenerateFlexItemForChild(
   nsPresContext* aPresContext,
   nsIFrame*      aChildFrame,
   const ReflowInput& aParentReflowInput,
   const FlexboxAxisTracker& aAxisTracker)
 {
   // Create temporary reflow state just for sizing -- to get hypothetical

--- a/layout/generic/nsFlexContainerFrame.h
+++ b/layout/generic/nsFlexContainerFrame.h
@@ -148,19 +148,16 @@ public:
     return true;
   }
 
   // nsContainerFrame overrides
   uint16_t CSSAlignmentForAbsPosChild(
             const ReflowInput& aChildRI,
             mozilla::LogicalAxis aLogicalAxis) const override;
 
-  // Flexbox-specific public methods
-  bool IsHorizontal();
-
   /**
    * Helper function to calculate packing space and initial offset of alignment
    * subjects in MainAxisPositionTracker() and CrossAxisPositionTracker() for
    * space-between, space-around, and space-evenly.
    *    * @param aNumThingsToPack             Number of alignment subjects.
    * @param aAlignVal                    Value for align-self or justify-self.
    * @param aFirstSubjectOffset          Outparam for first subject offset.
    * @param aNumPackingSpacesRemaining   Outparam for number of equal-sized