--- a/dom/html/HTMLIFrameElement.cpp
+++ b/dom/html/HTMLIFrameElement.cpp
@@ -96,68 +96,39 @@ HTMLIFrameElement::ParseAttribute(int32_
   }
 
   return nsGenericHTMLFrameElement::ParseAttribute(aNamespaceID, aAttribute,
                                                    aValue, aResult);
 }
 
 void
 HTMLIFrameElement::MapAttributesIntoRule(const nsMappedAttributes* aAttributes,
-                                         GenericSpecifiedValues* aGenericData)
+                                         GenericSpecifiedValues* aData)
 {
-  nsRuleData* aData = aGenericData->AsRuleData();
-  if (aData->mSIDs & NS_STYLE_INHERIT_BIT(Border)) {
+  if (aData->ShouldComputeStyleStruct(NS_STYLE_INHERIT_BIT(Border))) {
     // frameborder: 0 | 1 (| NO | YES in quirks mode)
     // If frameborder is 0 or No, set border to 0
     // else leave it as the value set in html.css
     const nsAttrValue* value = aAttributes->GetAttr(nsGkAtoms::frameborder);
     if (value && value->Type() == nsAttrValue::eEnum) {
       int32_t frameborder = value->GetEnumValue();
       if (NS_STYLE_FRAME_0 == frameborder ||
           NS_STYLE_FRAME_NO == frameborder ||
           NS_STYLE_FRAME_OFF == frameborder) {
-        nsCSSValue* borderLeftWidth = aData->ValueForBorderLeftWidth();
-        if (borderLeftWidth->GetUnit() == eCSSUnit_Null)
-          borderLeftWidth->SetFloatValue(0.0f, eCSSUnit_Pixel);
-        nsCSSValue* borderRightWidth = aData->ValueForBorderRightWidth();
-        if (borderRightWidth->GetUnit() == eCSSUnit_Null)
-          borderRightWidth->SetFloatValue(0.0f, eCSSUnit_Pixel);
-        nsCSSValue* borderTopWidth = aData->ValueForBorderTopWidth();
-        if (borderTopWidth->GetUnit() == eCSSUnit_Null)
-          borderTopWidth->SetFloatValue(0.0f, eCSSUnit_Pixel);
-        nsCSSValue* borderBottomWidth = aData->ValueForBorderBottomWidth();
-        if (borderBottomWidth->GetUnit() == eCSSUnit_Null)
-          borderBottomWidth->SetFloatValue(0.0f, eCSSUnit_Pixel);
+        aData->SetPixelValueIfUnset(eCSSProperty_border_top_width, 0.0f);
+        aData->SetPixelValueIfUnset(eCSSProperty_border_right_width, 0.0f);
+        aData->SetPixelValueIfUnset(eCSSProperty_border_bottom_width, 0.0f);
+        aData->SetPixelValueIfUnset(eCSSProperty_border_left_width, 0.0f);
       }
     }
   }
-  if (aData->mSIDs & NS_STYLE_INHERIT_BIT(Position)) {
-    // width: value
-    nsCSSValue* width = aData->ValueForWidth();
-    if (width->GetUnit() == eCSSUnit_Null) {
-      const nsAttrValue* value = aAttributes->GetAttr(nsGkAtoms::width);
-      if (value && value->Type() == nsAttrValue::eInteger)
-        width->SetFloatValue((float)value->GetIntegerValue(), eCSSUnit_Pixel);
-      else if (value && value->Type() == nsAttrValue::ePercent)
-        width->SetPercentValue(value->GetPercentValue());
-    }
 
-    // height: value
-    nsCSSValue* height = aData->ValueForHeight();
-    if (height->GetUnit() == eCSSUnit_Null) {
-      const nsAttrValue* value = aAttributes->GetAttr(nsGkAtoms::height);
-      if (value && value->Type() == nsAttrValue::eInteger)
-        height->SetFloatValue((float)value->GetIntegerValue(), eCSSUnit_Pixel);
-      else if (value && value->Type() == nsAttrValue::ePercent)
-        height->SetPercentValue(value->GetPercentValue());
-    }
-  }
-
-  nsGenericHTMLElement::MapImageAlignAttributeInto(aAttributes, aGenericData);
-  nsGenericHTMLElement::MapCommonAttributesInto(aAttributes, aGenericData);
+  nsGenericHTMLElement::MapImageSizeAttributesInto(aAttributes, aData);
+  nsGenericHTMLElement::MapImageAlignAttributeInto(aAttributes, aData);
+  nsGenericHTMLElement::MapCommonAttributesInto(aAttributes, aData);
 }
 
 NS_IMETHODIMP_(bool)
 HTMLIFrameElement::IsAttributeMapped(const nsIAtom* aAttribute) const
 {
   static const MappedAttributeEntry attributes[] = {
     { &nsGkAtoms::width },
     { &nsGkAtoms::height },