--- a/dom/base/nsXMLContentSerializer.cpp
+++ b/dom/base/nsXMLContentSerializer.cpp
@@ -667,20 +667,16 @@ nsXMLContentSerializer::SerializeAttr(co
           break;
         }
       } else if (*iCurr == char16_t('"')) {
         bIncludesDouble = true;
         if (bIncludesSingle) {
           break;
         }
       }
-      // if both have been found we don't need to search further
-      if (bIncludesDouble && bIncludesSingle) {
-        break;
-      }
     }
 
     // Delimiter and escaping is according to the following table
     //    bIncludesDouble     bIncludesSingle     Delimiter       Escape Double Quote
     //    FALSE               FALSE               "               FALSE
     //    FALSE               TRUE                "               FALSE
     //    TRUE                FALSE               '               FALSE
     //    TRUE                TRUE                "               TRUE