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