diff --git a/layout/generic/nsGfxScrollFrame.cpp b/layout/generic/nsGfxScrollFrame.cpp
index af065c2906f8..e14d2a8f633f 100644
--- a/layout/generic/nsGfxScrollFrame.cpp
+++ b/layout/generic/nsGfxScrollFrame.cpp
@@ -4918,11 +4918,9 @@ void ScrollFrameHelper::PostOverflowEvent()
   rpc->AddWillPaintObserver(mAsyncScrollPortEvent.get());
 }
 
-bool
-ScrollFrameHelper::IsPhysicalLTR() const
+nsIFrame*
+ScrollFrameHelper::GetFrameForDir() const
 {
-  //TODO make bidi code set these from preferences
-
   nsIFrame *frame = mOuter;
   // XXX This is a bit on the slow side.
   if (mIsRoot) {
@@ -4946,8 +4944,7 @@ ScrollFrameHelper::IsPhysicalLTR() const
     }
   }
 
-  WritingMode wm = frame->GetWritingMode();
-  return wm.IsVertical() ? wm.IsVerticalLR() : wm.IsBidiLTR();
+  return frame;
 }
 
 bool
@@ -5822,7 +5819,7 @@ ScrollFrameHelper::GetScrolledFrameDir() const
     }
   }
 
-  return IsPhysicalLTR() ? NS_STYLE_DIRECTION_LTR : NS_STYLE_DIRECTION_RTL;
+  return IsBidiLTR() ? NS_STYLE_DIRECTION_LTR : NS_STYLE_DIRECTION_RTL;
 }
 
 nsRect
diff --git a/layout/generic/nsGfxScrollFrame.h b/layout/generic/nsGfxScrollFrame.h
index d32e7ae162b3..cf3bff41533e 100644
--- a/layout/generic/nsGfxScrollFrame.h
+++ b/layout/generic/nsGfxScrollFrame.h
@@ -329,7 +329,19 @@ public:
   nsMargin GetDesiredScrollbarSizes(nsBoxLayoutState* aState);
   nscoord GetNondisappearingScrollbarWidth(nsBoxLayoutState* aState,
                                            mozilla::WritingMode aVerticalWM);
-  bool IsPhysicalLTR() const;
+  bool IsPhysicalLTR() const {
+    WritingMode wm = GetFrameForDir()->GetWritingMode();
+    return wm.IsVertical() ? wm.IsVerticalLR() : wm.IsBidiLTR();
+  }
+  bool IsBidiLTR() const {
+    nsIFrame* frame = GetFrameForDir();
+    return frame->StyleVisibility()->mDirection == NS_STYLE_DIRECTION_LTR;
+  }
+private:
+  nsIFrame* GetFrameForDir() const; // helper for Is{Physical,Bidi}LTR to find
+                                    // the frame whose directionality we use
+
+public:
   bool IsScrollbarOnRight() const;
   bool IsScrollingActive(nsDisplayListBuilder* aBuilder) const;
   bool IsMaybeScrollingActive() const;