firefox and acroread menubar colours wrong on suse 11.3

I am noting a funny (and sort of annoying behaviour) when using firefox and acrobat reader in a fvmw session under suse 11.3 (newly installed).

The topmost menu bar (File Edit …) has white text onto black background, although I do not have any X resource in .Xdefaults which makes that. The same (hardly legible) colour applies to all pull down menus, and for acrobat also to the bookmark window.

The remaining menu bars and widget are normal (black on light grey).

This occurs in fvwm sessions (which I WANT to use) but not in KDE sessions. There is nothing in the fvwm config nor in .Xdefaults which is asking for white foreground and black background (and anyhow I would not know how to apply them to firefox and acroread … editres does not get a widget tree).

According to the fvwm author it is not an fvwm problem. He points out to a colormap problem, but I am not aware to be using colormap-intensive applications.

I tried a xwininfo on the new system and on my old suse 9.2 one and the only difference I found is that for both I get Visual Class: TrueColor. The old one has Depth: 16, and the new one Depth: 24.

I found an easy way to change depth (added DefaultDepth 16 in /etc/X11/xorg.conf.d/50-screen.conf, restarted and checked), but even with depth 16 under 11.3 I get the white on black bars.