Gnusto - Interpreter for adventure games, ancient and modern, in the Z-machine format. - http://gnusto.mozdev.org
Xulmine - A project at mozdev.org that provides the famous Minesweeper-Game as extension for the Mozilla Browser. - http://xulmine.mozdev.org/
Amoeba role playing game engine - A classic role playing game engine created completely in XUL, JS, XBL, and CSS. In the classic style of early Final Fantasy games. Development still in progress. - http://sourceforge.net/projects/amoebarpg/