I have 2 console.log commands in the multiline firefox console and I execute them (cntrl+enter). It looks like there is only 1 undefined return value but this value is either after the first log or the second log - (I assume it is random or 'asynchronous'). Aside: during the question my tab crashed in firefox - seemingly the second time I've seen this recently.
console.log("hello")
console.log("sailor")