diff --git a/embedding/components/printingui/ipc/PPrintingTypes.ipdlh b/embedding/components/printingui/ipc/PPrintingTypes.ipdlh
index 8be8b2509360..084047bafe4c 100644
--- a/embedding/components/printingui/ipc/PPrintingTypes.ipdlh
+++ b/embedding/components/printingui/ipc/PPrintingTypes.ipdlh
@@ -118,6 +118,8 @@ struct PrintData {
    */
   float widthScale;
   float heightScale;
+  double adjustedPaperWidth;
+  double adjustedPaperHeight;
 };
 
 } // namespace embedding
diff --git a/widget/cocoa/nsPrintDialogX.mm b/widget/cocoa/nsPrintDialogX.mm
index 949899a0e3ce..a6d58d5bfb4b 100644
--- a/widget/cocoa/nsPrintDialogX.mm
+++ b/widget/cocoa/nsPrintDialogX.mm
@@ -145,7 +145,18 @@ nsPrintDialogServiceX::Show(nsPIDOMWindowOuter *aParent, nsIPrintSettings *aSett
       [dict setObject: [NSNumber numberWithFloat: 1]
                forKey: NSPrintScalingFactor];
     }
+    // Set the scaling factor to 100% in the NSPrintInfo
+    // object so that it will not affect the paper size
+    // retrieved from the PMPageFormat routines.
+    [copy setScalingFactor:1.0];
+  } else {
+    aSettings->SetScaling([copy scalingFactor]);
   }
+
+  // Set the adjusted paper size now that we've updated
+  // the scaling factor.
+  settingsX->InitAdjustedPaperSize();
+
   [copy release];
 
   int16_t pageRange;
diff --git a/widget/cocoa/nsPrintOptionsX.mm b/widget/cocoa/nsPrintOptionsX.mm
index a044ed422bc2..d9aa17b42ec1 100644
--- a/widget/cocoa/nsPrintOptionsX.mm
+++ b/widget/cocoa/nsPrintOptionsX.mm
@@ -71,6 +71,11 @@ nsPrintOptionsX::SerializeToPrintData(nsIPrintSettings* aSettings,
     return NS_ERROR_FAILURE;
   }
 
+  double adjustedWidth, adjustedHeight;
+  settingsX->GetAdjustedPaperSize(&adjustedWidth, &adjustedHeight);
+  data->adjustedPaperWidth() = adjustedWidth;
+  data->adjustedPaperHeight() = adjustedHeight;
+
   NSDictionary* dict = [printInfo dictionary];
   if (NS_WARN_IF(!dict)) {
     return NS_ERROR_FAILURE;
@@ -285,6 +290,9 @@ nsPrintOptionsX::DeserializeToPrintSettings(const PrintData& data,
   settingsX->SetCocoaPrintInfo(newPrintInfo);
   [newPrintInfo release];
 
+  settingsX->SetAdjustedPaperSize(data.adjustedPaperWidth(),
+                                  data.adjustedPaperHeight());
+
   return NS_OK;
 }
 
diff --git a/widget/cocoa/nsPrintSettingsX.h b/widget/cocoa/nsPrintSettingsX.h
index 9ab776126980..1d755b25057d 100644
--- a/widget/cocoa/nsPrintSettingsX.h
+++ b/widget/cocoa/nsPrintSettingsX.h
@@ -25,6 +25,15 @@ public:
   void SetCocoaPrintInfo(NSPrintInfo* aPrintInfo);
   virtual nsresult ReadPageFormatFromPrefs();
   virtual nsresult WritePageFormatToPrefs();
+  virtual nsresult GetEffectivePageSize(double *aWidth,
+      double *aHeight) override;
+
+  // In addition to setting the paper width and height, these
+  // overrides set the adjusted width and height returned from
+  // GetEffectivePageSize. This is needed when a paper size is
+  // set manually without using a print dialog a la reftest-print.
+  virtual nsresult SetPaperWidth(double aPaperWidth) override;
+  virtual nsresult SetPaperHeight(double aPaperWidth) override;
 
   PMPrintSettings GetPMPrintSettings();
   PMPrintSession GetPMPrintSession();
@@ -35,9 +44,16 @@ public:
   // Should be called whenever mPageFormat is initialized or overwritten.
   nsresult InitUnwriteableMargin();
 
+  // Re-initialize mAdjustedPaper{Width,Height} with values from mPageFormat.
+  // Should be called whenever mPageFormat is initialized or overwritten.
+  nsresult InitAdjustedPaperSize();
+
   void SetInchesScale(float aWidthScale, float aHeightScale);
   void GetInchesScale(float *aWidthScale, float *aHeightScale);
 
+  void SetAdjustedPaperSize(double aWidth, double aHeight);
+  void GetAdjustedPaperSize(double *aWidth, double *aHeight);
+
 protected:
   virtual ~nsPrintSettingsX();
 
@@ -57,6 +73,8 @@ protected:
   // paper size units to inches
   float mWidthScale;
   float mHeightScale;
+  double mAdjustedPaperWidth;
+  double mAdjustedPaperHeight;
 };
 
 NS_DEFINE_STATIC_IID_ACCESSOR(nsPrintSettingsX, NS_PRINTSETTINGSX_IID)
diff --git a/widget/cocoa/nsPrintSettingsX.mm b/widget/cocoa/nsPrintSettingsX.mm
index bf2302161204..73a8e78d2b1c 100644
--- a/widget/cocoa/nsPrintSettingsX.mm
+++ b/widget/cocoa/nsPrintSettingsX.mm
@@ -68,6 +68,7 @@ nsresult nsPrintSettingsX::Init()
   NS_OBJC_BEGIN_TRY_ABORT_BLOCK_NSRESULT;
 
   InitUnwriteableMargin();
+  InitAdjustedPaperSize();
 
   return NS_OK;
 
@@ -94,6 +95,23 @@ NS_IMETHODIMP nsPrintSettingsX::InitUnwriteableMargin()
   NS_OBJC_END_TRY_ABORT_BLOCK_NSRESULT;  
 }
 
+NS_IMETHODIMP nsPrintSettingsX::InitAdjustedPaperSize()
+{
+  NS_OBJC_BEGIN_TRY_ABORT_BLOCK_NSRESULT;
+
+  PMPageFormat pageFormat = GetPMPageFormat();
+
+  PMRect paperRect;
+  ::PMGetAdjustedPaperRect(pageFormat, &paperRect);
+
+  mAdjustedPaperWidth = paperRect.right - paperRect.left;
+  mAdjustedPaperHeight = paperRect.bottom - paperRect.top;
+
+  return NS_OK;
+
+  NS_OBJC_END_TRY_ABORT_BLOCK_NSRESULT;
+}
+
 void
 nsPrintSettingsX::SetCocoaPrintInfo(NSPrintInfo* aPrintInfo)
 {
@@ -206,8 +224,10 @@ nsPrintSettingsX::SetPMPageFormat(PMPageFormat aPageFormat)
 void
 nsPrintSettingsX::SetInchesScale(float aWidthScale, float aHeightScale)
 {
-  mWidthScale = aWidthScale;
-  mHeightScale = aHeightScale;
+  if (aWidthScale > 0 && aHeightScale > 0) {
+    mWidthScale = aWidthScale;
+    mHeightScale = aHeightScale;
+  }
 }
 
 void
@@ -216,3 +236,37 @@ nsPrintSettingsX::GetInchesScale(float *aWidthScale, float *aHeightScale)
   *aWidthScale = mWidthScale;
   *aHeightScale = mHeightScale;
 }
+
+NS_IMETHODIMP nsPrintSettingsX::SetPaperWidth(double aPaperWidth)
+{
+  mPaperWidth = aPaperWidth;
+  mAdjustedPaperWidth = aPaperWidth * mWidthScale;
+  return NS_OK;
+}
+
+NS_IMETHODIMP nsPrintSettingsX::SetPaperHeight(double aPaperHeight)
+{
+  mPaperHeight = aPaperHeight;
+  mAdjustedPaperHeight = aPaperHeight * mHeightScale;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsPrintSettingsX::GetEffectivePageSize(double *aWidth, double *aHeight)
+{
+  *aWidth  = NS_INCHES_TO_TWIPS(mAdjustedPaperWidth / mWidthScale);
+  *aHeight = NS_INCHES_TO_TWIPS(mAdjustedPaperHeight / mHeightScale);
+  return NS_OK;
+}
+
+void nsPrintSettingsX::SetAdjustedPaperSize(double aWidth, double aHeight)
+{
+  mAdjustedPaperWidth = aWidth;
+  mAdjustedPaperHeight = aHeight;
+}
+
+void nsPrintSettingsX::GetAdjustedPaperSize(double *aWidth, double *aHeight)
+{
+  *aWidth = mAdjustedPaperWidth;
+  *aHeight = mAdjustedPaperHeight;
+}