Mozilla Roadmap

Mozilla Browser Development Team (Netscape Communicator 5.0)
chose the library
GTK + as the main one for development under XWindow,
thus replacing the commercial Motif.

The GTK+ library was created with
development of a graphic editor GIMP
and is now used in the project GNOME
(development of a free graphical environment for UNIX).

Details on the mozilla.org, MozillaZine.

Source: linux.org.ru