I have noted this in several of the 'child' windows of mozilla. It looks like the text in the window is slightly too large for the window, i.e. it doesn't quite fit. An example when downloading flash plug-in, I get a little window which has the following buttons. 'Close', 'Pause' 'Launch File' 'Show Location'. On my screen the 'n' of 'show location' is only half seen as the rest of the 'n' is beyond the window frame. These text misfits are not consistently reproducible. Version 2002032803.
the particular example mentioned (the download dialog) is bug 79889. as to the general point - there are still a bunch of other dialogs ("child windows") with this problem, but I think they're all covered by existing bugs in bugzilla. *** This bug has been marked as a duplicate of 79889 ***