diff --git a/mozilla/content/base/src/nsHTMLContentSerializer.cpp b/mozilla/content/base/src/nsHTMLContentSerializer.cpp
index de1408b611b..b14a8bf5046 100644
--- a/mozilla/content/base/src/nsHTMLContentSerializer.cpp
+++ b/mozilla/content/base/src/nsHTMLContentSerializer.cpp
@@ -360,7 +360,9 @@ nsHTMLContentSerializer::SerializeAttributes(nsIContent* aContent,
         aContent->GetDocument(*getter_AddRefs(document));
         if (document) {
           nsCOMPtr<nsIURI> uri;
-          document->GetDocumentURL(getter_AddRefs(uri));
+          document->GetBaseURL(*getter_AddRefs(uri));
+          if (!uri)
+            document->GetDocumentURL(getter_AddRefs(uri));
           if (uri) {
             nsAutoString absURI;
             rv = NS_MakeAbsoluteURI(absURI, valueStr, uri);