Only WebKit and Gecko based browsers fully support Glade/Gtk+ due to incomplete implementation of various CSS features.
OS.js can also be deployed standalone, either running in a browser or on top of X11 as a complete Graphical Environment.
The information about this project has been moved to GitHub Pages.
Try the latest version on my live demo server.
This post is still open for comments, bug-reports, name-changes and other suggestions.
Public source-code was released in January 2013
Update November 2013: I have started working on version 2.0. Completely rewritten from scratch with a ton of improvments, a lot smaller and faster. More information here.