--- a/layout/base/nsLayoutUtils.cpp
+++ b/layout/base/nsLayoutUtils.cpp
@@ -1923,32 +1923,36 @@ nsLayoutUtils::GetTextShadowRectsUnion(c
 
     resultRect.UnionRect(resultRect, tmpRect);
   }
   return resultRect;
 }
 
 nsresult
 nsLayoutUtils::GetFontMetricsForFrame(const nsIFrame* aFrame,
-                                      nsFontMetrics** aFontMetrics)
+                                      nsFontMetrics** aFontMetrics,
+                                      float aInflation)
 {
   return nsLayoutUtils::GetFontMetricsForStyleContext(aFrame->GetStyleContext(),
-                                                      aFontMetrics);
+                                                      aFontMetrics,
+                                                      aInflation);
 }
 
 nsresult
 nsLayoutUtils::GetFontMetricsForStyleContext(nsStyleContext* aStyleContext,
-                                             nsFontMetrics** aFontMetrics)
+                                             nsFontMetrics** aFontMetrics,
+                                             float aInflation)
 {
   // pass the user font set object into the device context to pass along to CreateFontGroup
   gfxUserFontSet* fs = aStyleContext->PresContext()->GetUserFontSet();
 
+  nsFont font = aStyleContext->GetStyleFont()->mFont;
+  font.size = NSToCoordRound(font.size * aInflation);
   return aStyleContext->PresContext()->DeviceContext()->GetMetricsFor(
-                  aStyleContext->GetStyleFont()->mFont,
-                  aStyleContext->GetStyleVisibility()->mLanguage,
+                  font, aStyleContext->GetStyleVisibility()->mLanguage,
                   fs, *aFontMetrics);
 }
 
 nsIFrame*
 nsLayoutUtils::FindChildContainingDescendant(nsIFrame* aParent, nsIFrame* aDescendantFrame)
 {
   nsIFrame* result = aDescendantFrame;
 

--- a/layout/base/nsLayoutUtils.h
+++ b/layout/base/nsLayoutUtils.h
@@ -737,29 +737,33 @@ public:
   static nsRect GetTextShadowRectsUnion(const nsRect& aTextAndDecorationsRect,
                                         nsIFrame* aFrame,
                                         PRUint32 aFlags = 0);
 
   /**
    * Get the font metrics corresponding to the frame's style data.
    * @param aFrame the frame
    * @param aFontMetrics the font metrics result
+   * @param aSizeInflation number to multiply font size by
    * @return success or failure code
    */
   static nsresult GetFontMetricsForFrame(const nsIFrame* aFrame,
-                                         nsFontMetrics** aFontMetrics);
+                                         nsFontMetrics** aFontMetrics,
+                                         float aSizeInflation = 1.0f);
 
   /**
    * Get the font metrics corresponding to the given style data.
    * @param aStyleContext the style data
    * @param aFontMetrics the font metrics result
+   * @param aSizeInflation number to multiply font size by
    * @return success or failure code
    */
   static nsresult GetFontMetricsForStyleContext(nsStyleContext* aStyleContext,
-                                                nsFontMetrics** aFontMetrics);
+                                                nsFontMetrics** aFontMetrics,
+                                                float aSizeInflation = 1.0f);
 
   /**
    * Find the immediate child of aParent whose frame subtree contains
    * aDescendantFrame. Returns null if aDescendantFrame is not a descendant
    * of aParent.
    */
   static nsIFrame* FindChildContainingDescendant(nsIFrame* aParent, nsIFrame* aDescendantFrame);