The German app-default file /usr/X11R6/lib/X11/de/app-defaults/Netscape
contains a small glitch which causes the configuration editor display
"/builds/client/l10n_dev/temp/" instead of "Benutzername". The diff for the
corrected file looks like this:
< *MailServerInfo*form1*ServerUser.labelString: \
(this might get corrupted by this form)
The point is, that the filename at the end of the line is junk.
This will be fixed in netscape-4.74-2 - thanks for the report!