string fixes

layout/mathml/base/src/nsMathMLmfencedFrame.cpp

@@ -158,7 +158,7 @@ nsMathMLmfencedFrame::ReCreateFencesAndSeparators(nsIPresContext* aPresContext)
     data = value;
   }
   else if (NS_CONTENT_ATTR_NOT_THERE == rv)
-    data = ')'; // default as per the MathML REC
+    data = PRUnichar(')'); // default as per the MathML REC
   else
     data = nsAutoString();
 
@@ -178,7 +178,7 @@ nsMathMLmfencedFrame::ReCreateFencesAndSeparators(nsIPresContext* aPresContext)
     data = value;
   }
   else if (NS_CONTENT_ATTR_NOT_THERE == rv)
-    data = ','; // default as per the MathML REC
+    data = PRUnichar(','); // default as per the MathML REC
   else
     data = nsAutoString();