Your example has multiline text as VALUE of single line text field. Mozilla shows only the first line (on Windows). see Bug 51121. I think this is a bug. Mozilla should show all texts except line breaks.
changed the summary.
I think this is invalid; current behavior matches IE6, Opera 6 and NS 4.x, Word, Excel, and most other apps, and is probably as designed. cc UE for input, please reopen if otherwise.