This was noticed on a Debian system. With kgtk-qt3-trinity installed iceweasel, Etherape (possibly others) will not run : Gtk-ERROR **: GTK+ 2.x symbols detected. Using GTK+ 2.x and GTK+ 3 in the same process is not supported. Trace/breakpoint trap It is not known how it got on this particular system. kgtk-qt3-trinity is mentioned in bug reports as being marked for removal from TDE archives but is still there in 3.5.13.2 Adding this to /etc/apt/preferences blacklists it (create if it does not exist): Package: kgtk-qt3-trinity Pin: origin "" Pin-Priority: -1 David