Mozilla not opening new Windows

[gerhard.kroder@t-online.de (gk on the road...)]

no clue what's it about:

cannot open a mail/chat/adressbook window from inside Mozilla browser, 
i.e. neither via Ctrl-2/3/5 nor via "Window" pulldown menue. 
Furthermore, when started as mailclient (-mail) and reading emails, it 
doesn't [mouse-right-click: Open  link in new Window]. But new browser 
window can be opened (ctrl-1 or  pulldown menue).

Noticed this behaviour since a week or too, might be loger. All on a 
recent Sarge system, i386, of course with no such problems before.

Any ideas?

Gerhard