Fix for Firefox v42
Fix for Firefox v42

This is a follow up fixing the issue reported https://github.com/graphql/graphiql/issues/65

tim-steele/express-graphql,wincent/express-graphql,wincent/express-graphql,jamiehodge/express-graphql,tim-steele/express-graphql,graphql/express-graphql,tim-steele/express-graphql,jamiehodge/express-graphql,jamiehodge/express-graphql,wincent/express-graphql,graphql/express-graphql,graphql/express-graphql