Only perform horizontal alignment when there is room to do it

content/html/style/src/nsCSSLayout.cpp

@@ -212,6 +212,7 @@ nsCSSLayout::HorizontallyPlaceChildren(nsIPresContext* aCX,
                                        nscoord aLineWidth,
                                        nscoord aMaxWidth)
 {
+  if (aLineWidth < aMaxWidth) {
     PRIntn textAlign = aContainerStyle->mTextAlign;
     nscoord dx = 0;
     switch (textAlign) {
@@ -237,6 +238,7 @@ nsCSSLayout::HorizontallyPlaceChildren(nsIPresContext* aCX,
       kid->MoveTo(origin.x + dx, origin.y);
       kid->GetNextSibling(kid);
     }
+  }
 }
 
 /**

layout/html/style/src/nsCSSLayout.cpp

@@ -212,6 +212,7 @@ nsCSSLayout::HorizontallyPlaceChildren(nsIPresContext* aCX,
                                        nscoord aLineWidth,
                                        nscoord aMaxWidth)
 {
+  if (aLineWidth < aMaxWidth) {
     PRIntn textAlign = aContainerStyle->mTextAlign;
     nscoord dx = 0;
     switch (textAlign) {
@@ -237,6 +238,7 @@ nsCSSLayout::HorizontallyPlaceChildren(nsIPresContext* aCX,
       kid->MoveTo(origin.x + dx, origin.y);
       kid->GetNextSibling(kid);
     }
+  }
 }
 
 /**