diff --git a/mozilla/content/base/src/nsRuleNode.cpp b/mozilla/content/base/src/nsRuleNode.cpp
index 5d246e146c6..9d688900ec4 100644
--- a/mozilla/content/base/src/nsRuleNode.cpp
+++ b/mozilla/content/base/src/nsRuleNode.cpp
@@ -3275,18 +3275,18 @@ nsRuleNode::ComputeBackgroundData(nsStyleStruct* aStartStruct,
 
   // background-position: enum, length, percent (flags), inherit
   if (eCSSUnit_Percent == colorData.mBackPositionX.GetUnit()) {
-    bg->mBackgroundXPosition = (nscoord)(100.0f * colorData.mBackPositionX.GetPercentValue());
+    bg->mBackgroundXPosition.mFloat = colorData.mBackPositionX.GetPercentValue();
     bg->mBackgroundFlags |= NS_STYLE_BG_X_POSITION_PERCENT;
     bg->mBackgroundFlags &= ~NS_STYLE_BG_X_POSITION_LENGTH;
   }
   else if (colorData.mBackPositionX.IsLengthUnit()) {
-    bg->mBackgroundXPosition = CalcLength(colorData.mBackPositionX, nsnull, 
-                                          aContext, mPresContext, inherited);
+    bg->mBackgroundXPosition.mCoord = CalcLength(colorData.mBackPositionX, nsnull, 
+                                                 aContext, mPresContext, inherited);
     bg->mBackgroundFlags |= NS_STYLE_BG_X_POSITION_LENGTH;
     bg->mBackgroundFlags &= ~NS_STYLE_BG_X_POSITION_PERCENT;
   }
   else if (eCSSUnit_Enumerated == colorData.mBackPositionX.GetUnit()) {
-    bg->mBackgroundXPosition = (nscoord)colorData.mBackPositionX.GetIntValue();
+    bg->mBackgroundXPosition.mFloat = (float)colorData.mBackPositionX.GetIntValue() / 100.0f;
     bg->mBackgroundFlags |= NS_STYLE_BG_X_POSITION_PERCENT;
     bg->mBackgroundFlags &= ~NS_STYLE_BG_X_POSITION_LENGTH;
   }
@@ -3298,18 +3298,18 @@ nsRuleNode::ComputeBackgroundData(nsStyleStruct* aStartStruct,
   }
 
   if (eCSSUnit_Percent == colorData.mBackPositionY.GetUnit()) {
-    bg->mBackgroundYPosition = (nscoord)(100.0f * colorData.mBackPositionY.GetPercentValue());
+    bg->mBackgroundYPosition.mFloat = colorData.mBackPositionY.GetPercentValue();
     bg->mBackgroundFlags |= NS_STYLE_BG_Y_POSITION_PERCENT;
     bg->mBackgroundFlags &= ~NS_STYLE_BG_Y_POSITION_LENGTH;
   }
   else if (colorData.mBackPositionY.IsLengthUnit()) {
-    bg->mBackgroundYPosition = CalcLength(colorData.mBackPositionY, nsnull,
-                                          aContext, mPresContext, inherited);
+    bg->mBackgroundYPosition.mCoord = CalcLength(colorData.mBackPositionY, nsnull,
+                                                 aContext, mPresContext, inherited);
     bg->mBackgroundFlags |= NS_STYLE_BG_Y_POSITION_LENGTH;
     bg->mBackgroundFlags &= ~NS_STYLE_BG_Y_POSITION_PERCENT;
   }
   else if (eCSSUnit_Enumerated == colorData.mBackPositionY.GetUnit()) {
-    bg->mBackgroundYPosition = (nscoord)colorData.mBackPositionY.GetIntValue();
+    bg->mBackgroundYPosition.mFloat = (float)colorData.mBackPositionY.GetIntValue() / 100.0f;
     bg->mBackgroundFlags |= NS_STYLE_BG_Y_POSITION_PERCENT;
     bg->mBackgroundFlags &= ~NS_STYLE_BG_Y_POSITION_LENGTH;
   }
diff --git a/mozilla/content/base/src/nsStyleContext.cpp b/mozilla/content/base/src/nsStyleContext.cpp
index 26c5d2b7a1e..13428a4cd56 100644
--- a/mozilla/content/base/src/nsStyleContext.cpp
+++ b/mozilla/content/base/src/nsStyleContext.cpp
@@ -939,8 +939,8 @@ void nsStyleContext::DumpRegressionData(nsIPresContext* aPresContext, FILE* out,
     (int)bg->mBackgroundFlags,
     (int)bg->mBackgroundRepeat,
     (long)bg->mBackgroundColor,
-    (long)bg->mBackgroundXPosition,
-    (long)bg->mBackgroundYPosition,
+    (long)bg->mBackgroundXPosition.mCoord, // potentially lossy on some platforms
+    (long)bg->mBackgroundYPosition.mCoord, // potentially lossy on some platforms
     NS_ConvertUCS2toUTF8(bg->mBackgroundImage).get());
  
   // SPACING (ie. margin, padding, border, outline)
diff --git a/mozilla/content/shared/public/nsStyleStruct.h b/mozilla/content/shared/public/nsStyleStruct.h
index d832286c13d..dd99d7931b8 100644
--- a/mozilla/content/shared/public/nsStyleStruct.h
+++ b/mozilla/content/shared/public/nsStyleStruct.h
@@ -168,9 +168,15 @@ struct nsStyleBackground : public nsStyleStruct {
   PRUint8 mBackgroundOrigin       : 3; // [reset] See nsStyleConsts.h
   PRUint8 mBackgroundRepeat       : 4; // [reset] See nsStyleConsts.h
 
+  // Note: a member of this union is valid IFF the appropriate bit flag
+  // is set in mBackgroundFlags.
+  union {
+    nscoord mCoord;
+    float   mFloat;
+  } mBackgroundXPosition,         // [reset]
+    mBackgroundYPosition;         // [reset]
+
   nscolor mBackgroundColor;       // [reset]
-  nscoord mBackgroundXPosition;   // [reset]
-  nscoord mBackgroundYPosition;   // [reset]
   nsString mBackgroundImage;      // [reset] absolute url string
 
   PRBool IsTransparent() const
@@ -179,11 +185,6 @@ struct nsStyleBackground : public nsStyleStruct {
             (NS_STYLE_BG_COLOR_TRANSPARENT | NS_STYLE_BG_IMAGE_NONE)) ==
             (NS_STYLE_BG_COLOR_TRANSPARENT | NS_STYLE_BG_IMAGE_NONE);
   }
-
-  PRBool IsPositioned() const
-  {
-    return mBackgroundXPosition != 0 || mBackgroundYPosition != 0;
-  }
 };
 
 #define BORDER_COLOR_DEFINED      0x80  
diff --git a/mozilla/content/shared/src/nsStyleStruct.cpp b/mozilla/content/shared/src/nsStyleStruct.cpp
index 51a4616708e..90474e8d897 100644
--- a/mozilla/content/shared/src/nsStyleStruct.cpp
+++ b/mozilla/content/shared/src/nsStyleStruct.cpp
@@ -974,9 +974,7 @@ nsStyleBackground::nsStyleBackground(nsIPresContext* aPresContext)
     mBackgroundClip(NS_STYLE_BG_CLIP_BORDER),
     mBackgroundInlinePolicy(NS_STYLE_BG_INLINE_POLICY_CONTINUOUS),
     mBackgroundOrigin(NS_STYLE_BG_ORIGIN_PADDING),
-    mBackgroundRepeat(NS_STYLE_BG_REPEAT_XY),
-    mBackgroundXPosition(0),
-    mBackgroundYPosition(0)
+    mBackgroundRepeat(NS_STYLE_BG_REPEAT_XY)
 {
   aPresContext->GetDefaultBackgroundColor(&mBackgroundColor);
 }
@@ -988,9 +986,9 @@ nsStyleBackground::nsStyleBackground(const nsStyleBackground& aSource)
     mBackgroundInlinePolicy(aSource.mBackgroundInlinePolicy),
     mBackgroundOrigin(aSource.mBackgroundOrigin),
     mBackgroundRepeat(aSource.mBackgroundRepeat),
-    mBackgroundColor(aSource.mBackgroundColor),
     mBackgroundXPosition(aSource.mBackgroundXPosition),
     mBackgroundYPosition(aSource.mBackgroundYPosition),
+    mBackgroundColor(aSource.mBackgroundColor),
     mBackgroundImage(aSource.mBackgroundImage)
 {
 }
@@ -1007,12 +1005,18 @@ nsChangeHint nsStyleBackground::CalcDifference(const nsStyleBackground& aOther)
       (mBackgroundFlags == aOther.mBackgroundFlags) &&
       (mBackgroundRepeat == aOther.mBackgroundRepeat) &&
       (mBackgroundColor == aOther.mBackgroundColor) &&
-      (mBackgroundXPosition == aOther.mBackgroundXPosition) &&
-      (mBackgroundYPosition == aOther.mBackgroundYPosition) &&
       (mBackgroundClip == aOther.mBackgroundClip) &&
       (mBackgroundInlinePolicy == aOther.mBackgroundInlinePolicy) &&
       (mBackgroundOrigin == aOther.mBackgroundOrigin) &&
-      (mBackgroundImage == aOther.mBackgroundImage))
+      (mBackgroundImage == aOther.mBackgroundImage) &&
+      ((!(mBackgroundFlags & NS_STYLE_BG_X_POSITION_PERCENT) ||
+       (mBackgroundXPosition.mFloat == aOther.mBackgroundXPosition.mFloat)) &&
+       (!(mBackgroundFlags & NS_STYLE_BG_X_POSITION_LENGTH) ||
+        (mBackgroundXPosition.mCoord == aOther.mBackgroundXPosition.mCoord))) &&
+      ((!(mBackgroundFlags & NS_STYLE_BG_Y_POSITION_PERCENT) ||
+       (mBackgroundYPosition.mFloat == aOther.mBackgroundYPosition.mFloat)) &&
+       (!(mBackgroundFlags & NS_STYLE_BG_Y_POSITION_LENGTH) ||
+        (mBackgroundYPosition.mCoord == aOther.mBackgroundYPosition.mCoord))))
     return NS_STYLE_HINT_NONE;
   return NS_STYLE_HINT_VISUAL;
 }
diff --git a/mozilla/layout/base/nsCSSRendering.cpp b/mozilla/layout/base/nsCSSRendering.cpp
index 627916d8edd..60d446d824e 100644
--- a/mozilla/layout/base/nsCSSRendering.cpp
+++ b/mozilla/layout/base/nsCSSRendering.cpp
@@ -2397,14 +2397,16 @@ ComputeBackgroundAnchorPoint(const nsStyleBackground& aColor,
 {
   nscoord x;
   if (NS_STYLE_BG_X_POSITION_LENGTH & aColor.mBackgroundFlags) {
-    x = aColor.mBackgroundXPosition;
+    x = aColor.mBackgroundXPosition.mCoord;
+  }
+  else if (NS_STYLE_BG_X_POSITION_PERCENT & aColor.mBackgroundFlags) {
+    PRFloat64 percent = PRFloat64(aColor.mBackgroundXPosition.mFloat);
+    nscoord tilePos = nscoord(percent * PRFloat64(aTileWidth));
+    nscoord boxPos = nscoord(percent * PRFloat64(aOriginBounds.width));
+    x = boxPos - tilePos;
   }
   else {
-    nscoord t = aColor.mBackgroundXPosition;
-    float pct = float(t) / 100.0f;
-    nscoord tilePos = nscoord(pct * aTileWidth);
-    nscoord boxPos = nscoord(pct * aOriginBounds.width);
-    x = boxPos - tilePos;
+    x = 0;
   }
   x += aOriginBounds.x - aClipBounds.x;
   if (NS_STYLE_BG_REPEAT_X & aColor.mBackgroundRepeat) {
@@ -2434,14 +2436,16 @@ ComputeBackgroundAnchorPoint(const nsStyleBackground& aColor,
 
   nscoord y;
   if (NS_STYLE_BG_Y_POSITION_LENGTH & aColor.mBackgroundFlags) {
-    y = aColor.mBackgroundYPosition;
+    y = aColor.mBackgroundYPosition.mCoord;
+  }
+  else if (NS_STYLE_BG_Y_POSITION_PERCENT & aColor.mBackgroundFlags){
+    PRFloat64 percent = PRFloat64(aColor.mBackgroundYPosition.mFloat);
+    nscoord tilePos = nscoord(percent * PRFloat64(aTileHeight));
+    nscoord boxPos = nscoord(percent * PRFloat64(aOriginBounds.height));
+    y = boxPos - tilePos;
   }
   else {
-    nscoord t = aColor.mBackgroundYPosition;
-    float pct = float(t) / 100.0f;
-    nscoord tilePos = nscoord(pct * aTileHeight);
-    nscoord boxPos = nscoord(pct * aOriginBounds.height);
-    y = boxPos - tilePos;
+    y = 0;
   }
   y += aOriginBounds.y - aClipBounds.y;
   if (NS_STYLE_BG_REPEAT_Y & aColor.mBackgroundRepeat) {
diff --git a/mozilla/layout/html/style/src/nsCSSRendering.cpp b/mozilla/layout/html/style/src/nsCSSRendering.cpp
index 627916d8edd..60d446d824e 100644
--- a/mozilla/layout/html/style/src/nsCSSRendering.cpp
+++ b/mozilla/layout/html/style/src/nsCSSRendering.cpp
@@ -2397,14 +2397,16 @@ ComputeBackgroundAnchorPoint(const nsStyleBackground& aColor,
 {
   nscoord x;
   if (NS_STYLE_BG_X_POSITION_LENGTH & aColor.mBackgroundFlags) {
-    x = aColor.mBackgroundXPosition;
+    x = aColor.mBackgroundXPosition.mCoord;
+  }
+  else if (NS_STYLE_BG_X_POSITION_PERCENT & aColor.mBackgroundFlags) {
+    PRFloat64 percent = PRFloat64(aColor.mBackgroundXPosition.mFloat);
+    nscoord tilePos = nscoord(percent * PRFloat64(aTileWidth));
+    nscoord boxPos = nscoord(percent * PRFloat64(aOriginBounds.width));
+    x = boxPos - tilePos;
   }
   else {
-    nscoord t = aColor.mBackgroundXPosition;
-    float pct = float(t) / 100.0f;
-    nscoord tilePos = nscoord(pct * aTileWidth);
-    nscoord boxPos = nscoord(pct * aOriginBounds.width);
-    x = boxPos - tilePos;
+    x = 0;
   }
   x += aOriginBounds.x - aClipBounds.x;
   if (NS_STYLE_BG_REPEAT_X & aColor.mBackgroundRepeat) {
@@ -2434,14 +2436,16 @@ ComputeBackgroundAnchorPoint(const nsStyleBackground& aColor,
 
   nscoord y;
   if (NS_STYLE_BG_Y_POSITION_LENGTH & aColor.mBackgroundFlags) {
-    y = aColor.mBackgroundYPosition;
+    y = aColor.mBackgroundYPosition.mCoord;
+  }
+  else if (NS_STYLE_BG_Y_POSITION_PERCENT & aColor.mBackgroundFlags){
+    PRFloat64 percent = PRFloat64(aColor.mBackgroundYPosition.mFloat);
+    nscoord tilePos = nscoord(percent * PRFloat64(aTileHeight));
+    nscoord boxPos = nscoord(percent * PRFloat64(aOriginBounds.height));
+    y = boxPos - tilePos;
   }
   else {
-    nscoord t = aColor.mBackgroundYPosition;
-    float pct = float(t) / 100.0f;
-    nscoord tilePos = nscoord(pct * aTileHeight);
-    nscoord boxPos = nscoord(pct * aOriginBounds.height);
-    y = boxPos - tilePos;
+    y = 0;
   }
   y += aOriginBounds.y - aClipBounds.y;
   if (NS_STYLE_BG_REPEAT_Y & aColor.mBackgroundRepeat) {
diff --git a/mozilla/layout/style/nsRuleNode.cpp b/mozilla/layout/style/nsRuleNode.cpp
index 5d246e146c6..9d688900ec4 100644
--- a/mozilla/layout/style/nsRuleNode.cpp
+++ b/mozilla/layout/style/nsRuleNode.cpp
@@ -3275,18 +3275,18 @@ nsRuleNode::ComputeBackgroundData(nsStyleStruct* aStartStruct,
 
   // background-position: enum, length, percent (flags), inherit
   if (eCSSUnit_Percent == colorData.mBackPositionX.GetUnit()) {
-    bg->mBackgroundXPosition = (nscoord)(100.0f * colorData.mBackPositionX.GetPercentValue());
+    bg->mBackgroundXPosition.mFloat = colorData.mBackPositionX.GetPercentValue();
     bg->mBackgroundFlags |= NS_STYLE_BG_X_POSITION_PERCENT;
     bg->mBackgroundFlags &= ~NS_STYLE_BG_X_POSITION_LENGTH;
   }
   else if (colorData.mBackPositionX.IsLengthUnit()) {
-    bg->mBackgroundXPosition = CalcLength(colorData.mBackPositionX, nsnull, 
-                                          aContext, mPresContext, inherited);
+    bg->mBackgroundXPosition.mCoord = CalcLength(colorData.mBackPositionX, nsnull, 
+                                                 aContext, mPresContext, inherited);
     bg->mBackgroundFlags |= NS_STYLE_BG_X_POSITION_LENGTH;
     bg->mBackgroundFlags &= ~NS_STYLE_BG_X_POSITION_PERCENT;
   }
   else if (eCSSUnit_Enumerated == colorData.mBackPositionX.GetUnit()) {
-    bg->mBackgroundXPosition = (nscoord)colorData.mBackPositionX.GetIntValue();
+    bg->mBackgroundXPosition.mFloat = (float)colorData.mBackPositionX.GetIntValue() / 100.0f;
     bg->mBackgroundFlags |= NS_STYLE_BG_X_POSITION_PERCENT;
     bg->mBackgroundFlags &= ~NS_STYLE_BG_X_POSITION_LENGTH;
   }
@@ -3298,18 +3298,18 @@ nsRuleNode::ComputeBackgroundData(nsStyleStruct* aStartStruct,
   }
 
   if (eCSSUnit_Percent == colorData.mBackPositionY.GetUnit()) {
-    bg->mBackgroundYPosition = (nscoord)(100.0f * colorData.mBackPositionY.GetPercentValue());
+    bg->mBackgroundYPosition.mFloat = colorData.mBackPositionY.GetPercentValue();
     bg->mBackgroundFlags |= NS_STYLE_BG_Y_POSITION_PERCENT;
     bg->mBackgroundFlags &= ~NS_STYLE_BG_Y_POSITION_LENGTH;
   }
   else if (colorData.mBackPositionY.IsLengthUnit()) {
-    bg->mBackgroundYPosition = CalcLength(colorData.mBackPositionY, nsnull,
-                                          aContext, mPresContext, inherited);
+    bg->mBackgroundYPosition.mCoord = CalcLength(colorData.mBackPositionY, nsnull,
+                                                 aContext, mPresContext, inherited);
     bg->mBackgroundFlags |= NS_STYLE_BG_Y_POSITION_LENGTH;
     bg->mBackgroundFlags &= ~NS_STYLE_BG_Y_POSITION_PERCENT;
   }
   else if (eCSSUnit_Enumerated == colorData.mBackPositionY.GetUnit()) {
-    bg->mBackgroundYPosition = (nscoord)colorData.mBackPositionY.GetIntValue();
+    bg->mBackgroundYPosition.mFloat = (float)colorData.mBackPositionY.GetIntValue() / 100.0f;
     bg->mBackgroundFlags |= NS_STYLE_BG_Y_POSITION_PERCENT;
     bg->mBackgroundFlags &= ~NS_STYLE_BG_Y_POSITION_LENGTH;
   }
diff --git a/mozilla/layout/style/nsStyleContext.cpp b/mozilla/layout/style/nsStyleContext.cpp
index 26c5d2b7a1e..13428a4cd56 100644
--- a/mozilla/layout/style/nsStyleContext.cpp
+++ b/mozilla/layout/style/nsStyleContext.cpp
@@ -939,8 +939,8 @@ void nsStyleContext::DumpRegressionData(nsIPresContext* aPresContext, FILE* out,
     (int)bg->mBackgroundFlags,
     (int)bg->mBackgroundRepeat,
     (long)bg->mBackgroundColor,
-    (long)bg->mBackgroundXPosition,
-    (long)bg->mBackgroundYPosition,
+    (long)bg->mBackgroundXPosition.mCoord, // potentially lossy on some platforms
+    (long)bg->mBackgroundYPosition.mCoord, // potentially lossy on some platforms
     NS_ConvertUCS2toUTF8(bg->mBackgroundImage).get());
  
   // SPACING (ie. margin, padding, border, outline)
diff --git a/mozilla/layout/style/nsStyleStruct.cpp b/mozilla/layout/style/nsStyleStruct.cpp
index 51a4616708e..90474e8d897 100644
--- a/mozilla/layout/style/nsStyleStruct.cpp
+++ b/mozilla/layout/style/nsStyleStruct.cpp
@@ -974,9 +974,7 @@ nsStyleBackground::nsStyleBackground(nsIPresContext* aPresContext)
     mBackgroundClip(NS_STYLE_BG_CLIP_BORDER),
     mBackgroundInlinePolicy(NS_STYLE_BG_INLINE_POLICY_CONTINUOUS),
     mBackgroundOrigin(NS_STYLE_BG_ORIGIN_PADDING),
-    mBackgroundRepeat(NS_STYLE_BG_REPEAT_XY),
-    mBackgroundXPosition(0),
-    mBackgroundYPosition(0)
+    mBackgroundRepeat(NS_STYLE_BG_REPEAT_XY)
 {
   aPresContext->GetDefaultBackgroundColor(&mBackgroundColor);
 }
@@ -988,9 +986,9 @@ nsStyleBackground::nsStyleBackground(const nsStyleBackground& aSource)
     mBackgroundInlinePolicy(aSource.mBackgroundInlinePolicy),
     mBackgroundOrigin(aSource.mBackgroundOrigin),
     mBackgroundRepeat(aSource.mBackgroundRepeat),
-    mBackgroundColor(aSource.mBackgroundColor),
     mBackgroundXPosition(aSource.mBackgroundXPosition),
     mBackgroundYPosition(aSource.mBackgroundYPosition),
+    mBackgroundColor(aSource.mBackgroundColor),
     mBackgroundImage(aSource.mBackgroundImage)
 {
 }
@@ -1007,12 +1005,18 @@ nsChangeHint nsStyleBackground::CalcDifference(const nsStyleBackground& aOther)
       (mBackgroundFlags == aOther.mBackgroundFlags) &&
       (mBackgroundRepeat == aOther.mBackgroundRepeat) &&
       (mBackgroundColor == aOther.mBackgroundColor) &&
-      (mBackgroundXPosition == aOther.mBackgroundXPosition) &&
-      (mBackgroundYPosition == aOther.mBackgroundYPosition) &&
       (mBackgroundClip == aOther.mBackgroundClip) &&
       (mBackgroundInlinePolicy == aOther.mBackgroundInlinePolicy) &&
       (mBackgroundOrigin == aOther.mBackgroundOrigin) &&
-      (mBackgroundImage == aOther.mBackgroundImage))
+      (mBackgroundImage == aOther.mBackgroundImage) &&
+      ((!(mBackgroundFlags & NS_STYLE_BG_X_POSITION_PERCENT) ||
+       (mBackgroundXPosition.mFloat == aOther.mBackgroundXPosition.mFloat)) &&
+       (!(mBackgroundFlags & NS_STYLE_BG_X_POSITION_LENGTH) ||
+        (mBackgroundXPosition.mCoord == aOther.mBackgroundXPosition.mCoord))) &&
+      ((!(mBackgroundFlags & NS_STYLE_BG_Y_POSITION_PERCENT) ||
+       (mBackgroundYPosition.mFloat == aOther.mBackgroundYPosition.mFloat)) &&
+       (!(mBackgroundFlags & NS_STYLE_BG_Y_POSITION_LENGTH) ||
+        (mBackgroundYPosition.mCoord == aOther.mBackgroundYPosition.mCoord))))
     return NS_STYLE_HINT_NONE;
   return NS_STYLE_HINT_VISUAL;
 }
diff --git a/mozilla/layout/style/nsStyleStruct.h b/mozilla/layout/style/nsStyleStruct.h
index d832286c13d..dd99d7931b8 100644
--- a/mozilla/layout/style/nsStyleStruct.h
+++ b/mozilla/layout/style/nsStyleStruct.h
@@ -168,9 +168,15 @@ struct nsStyleBackground : public nsStyleStruct {
   PRUint8 mBackgroundOrigin       : 3; // [reset] See nsStyleConsts.h
   PRUint8 mBackgroundRepeat       : 4; // [reset] See nsStyleConsts.h
 
+  // Note: a member of this union is valid IFF the appropriate bit flag
+  // is set in mBackgroundFlags.
+  union {
+    nscoord mCoord;
+    float   mFloat;
+  } mBackgroundXPosition,         // [reset]
+    mBackgroundYPosition;         // [reset]
+
   nscolor mBackgroundColor;       // [reset]
-  nscoord mBackgroundXPosition;   // [reset]
-  nscoord mBackgroundYPosition;   // [reset]
   nsString mBackgroundImage;      // [reset] absolute url string
 
   PRBool IsTransparent() const
@@ -179,11 +185,6 @@ struct nsStyleBackground : public nsStyleStruct {
             (NS_STYLE_BG_COLOR_TRANSPARENT | NS_STYLE_BG_IMAGE_NONE)) ==
             (NS_STYLE_BG_COLOR_TRANSPARENT | NS_STYLE_BG_IMAGE_NONE);
   }
-
-  PRBool IsPositioned() const
-  {
-    return mBackgroundXPosition != 0 || mBackgroundYPosition != 0;
-  }
 };
 
 #define BORDER_COLOR_DEFINED      0x80