--- a/toolkit/mozapps/downloads/DownloadUtils.jsm
+++ b/toolkit/mozapps/downloads/DownloadUtils.jsm
@@ -481,19 +481,22 @@ this.DownloadUtils = {
 
     // Don't try to format Infinity values using NumberFormat.
     if (aBytes === Infinity) {
       aBytes = "Infinity";
     } else {
       if (typeof Intl != "undefined") {
         aBytes = getLocaleNumberFormat(fractionDigits)
                    .format(aBytes);
-      } else if (gDecimalSymbol != ".") {
+      } else {
         // FIXME: Fall back to the old hack, will be fixed in bug 1200494.
-        aBytes = aBytes.toFixed(fractionDigits).replace(".", gDecimalSymbol);
+        aBytes = aBytes.toFixed(fractionDigits);
+        if (gDecimalSymbol != ".") {
+          aBytes = aBytes.replace(".", gDecimalSymbol);
+        }
       }
     }
 
     return [aBytes, gBundle.GetStringFromName(gStr.units[unitIndex])];
   },
 
   /**
    * Converts a number of seconds to the two largest units. Time values are