--- a/widget/gtk/nsNativeThemeGTK.cpp
+++ b/widget/gtk/nsNativeThemeGTK.cpp
@@ -144,29 +144,25 @@ static bool IsWidgetStateSafe(uint8_t* a
 static void SetWidgetStateSafe(uint8_t *aSafeVector,
                                uint8_t aWidgetType,
                                GtkWidgetState *aWidgetState)
 {
   uint8_t key = GetWidgetStateKey(aWidgetType, aWidgetState);
   aSafeVector[key >> 3] |= (1 << (key & 7));
 }
 
-static GtkTextDirection GetTextDirection(nsIFrame* aFrame)
+/* static */ GtkTextDirection
+nsNativeThemeGTK::GetTextDirection(nsIFrame* aFrame)
 {
-  if (!aFrame)
-    return GTK_TEXT_DIR_NONE;
-
-  switch (aFrame->StyleVisibility()->mDirection) {
-    case NS_STYLE_DIRECTION_RTL:
-      return GTK_TEXT_DIR_RTL;
-    case NS_STYLE_DIRECTION_LTR:
-      return GTK_TEXT_DIR_LTR;
-  }
-
-  return GTK_TEXT_DIR_NONE;
+  // IsFrameRTL() treats vertical-rl modes as right-to-left (in addition to
+  // horizontal text with direction=RTL), rather than just considering the
+  // text direction.  GtkTextDirection does not have distinct values for
+  // vertical writing modes, but considering the block flow direction is
+  // important for resizers and scrollbar elements, at least.
+  return IsFrameRTL(aFrame) ? GTK_TEXT_DIR_RTL : GTK_TEXT_DIR_LTR;
 }
 
 // Returns positive for negative margins (otherwise 0).
 gint
 nsNativeThemeGTK::GetTabMarginPixels(nsIFrame* aFrame)
 {
   nscoord margin =
     IsBottomTab(aFrame) ? aFrame->GetUsedMargin().top
@@ -1114,24 +1110,17 @@ NS_IMETHODIMP
 nsNativeThemeGTK::DrawWidgetBackground(nsRenderingContext* aContext,
                                        nsIFrame* aFrame,
                                        uint8_t aWidgetType,
                                        const nsRect& aRect,
                                        const nsRect& aDirtyRect)
 {
   GtkWidgetState state;
   WidgetNodeType gtkWidgetType;
-  // For resizer drawing, we want IsFrameRTL, which treats vertical-rl modes
-  // as right-to-left (in addition to horizontal text with direction=RTL),
-  // rather than just considering the text direction.
-  // This will make resizers on vertically-oriented elements render properly.
-  GtkTextDirection direction =
-    aWidgetType == NS_THEME_RESIZER
-    ? (IsFrameRTL(aFrame) ? GTK_TEXT_DIR_RTL : GTK_TEXT_DIR_LTR)
-    : GetTextDirection(aFrame);
+  GtkTextDirection direction = GetTextDirection(aFrame);
   gint flags;
   if (!GetGtkWidgetAndState(aWidgetType, aFrame, gtkWidgetType, &state,
                             &flags))
     return NS_OK;
 
   gfxContext* ctx = aContext->ThebesContext();
   nsPresContext *presContext = aFrame->PresContext();
 

--- a/widget/gtk/nsNativeThemeGTK.h
+++ b/widget/gtk/nsNativeThemeGTK.h
@@ -69,16 +69,17 @@ public:
                                              uint8_t aWidgetType) override;
 
   nsNativeThemeGTK();
 
 protected:
   virtual ~nsNativeThemeGTK();
 
 private:
+  GtkTextDirection GetTextDirection(nsIFrame* aFrame);
   gint GetTabMarginPixels(nsIFrame* aFrame);
   bool GetGtkWidgetAndState(uint8_t aWidgetType, nsIFrame* aFrame,
                             WidgetNodeType& aGtkWidgetType,
                             GtkWidgetState* aState, gint* aWidgetFlags);
   bool GetExtraSizeForWidget(nsIFrame* aFrame, uint8_t aWidgetType,
                                nsIntMargin* aExtra);
 
   void RefreshWidgetWindow(nsIFrame* aFrame);

--- a/widget/nsNativeTheme.cpp
+++ b/widget/nsNativeTheme.cpp
@@ -371,17 +371,17 @@ nsNativeTheme::IsDisabled(nsIFrame* aFra
 
   // For XML/XUL elements, an attribute must be equal to the literal
   // string "true" to be counted as true.  An empty string should _not_
   // be counted as true.
   return content->AttrValueIs(kNameSpaceID_None, nsGkAtoms::disabled,
                               NS_LITERAL_STRING("true"), eCaseMatters);
 }
 
-bool
+/* static */ bool
 nsNativeTheme::IsFrameRTL(nsIFrame* aFrame)
 {
   if (!aFrame) {
     return false;
   }
   WritingMode wm = aFrame->GetWritingMode();
   return !(wm.IsVertical() ? wm.IsVerticalLR() : wm.IsBidiLTR());
 }

--- a/widget/nsNativeTheme.h
+++ b/widget/nsNativeTheme.h
@@ -55,17 +55,17 @@ class nsNativeTheme : public nsITimerCal
   bool IsWidgetStyled(nsPresContext* aPresContext, nsIFrame* aFrame,
                         uint8_t aWidgetType);                                              
 
   // Accessors to widget-specific state information
 
   bool IsDisabled(nsIFrame* aFrame, mozilla::EventStates aEventStates);
 
   // RTL chrome direction
-  bool IsFrameRTL(nsIFrame* aFrame);
+  static bool IsFrameRTL(nsIFrame* aFrame);
 
   bool IsHTMLContent(nsIFrame *aFrame);
   
   // button:
   bool IsDefaultButton(nsIFrame* aFrame) {
     return CheckBooleanAttr(aFrame, nsGkAtoms::_default);
   }