Build no. 2000051608 This could be related to the oversized nature of them but single line text entry boxes can now take two lines before horizontally. To repeat, simply enter a long sentence in a single line text entry box.
I cannot verify this on Windows 2000 with 200051520. I tried entering a long string into the Find dialog, the subject field of a composition and the To: field of a composition. I saw nothing unusual.
I don't see this in NS verification build 51908. resolving as wfm, if you still see it please reopen with steps to reproduce.
I have looked at later builds and haven't seen any repeat of this behaviour. I think it is related to bug 39833. I think that the way moz handles t/type fonts in X could have created the problems.
verified wfm per Stefan above (leaving other issues to other bugs).
Mass removing self from CC list.
Now I feel sumb because I have to add back. Sorry for the spam.