There are two packages. One is gtk-gui - this is the GUI framework, based heavily on the framework in the Tk browser, but somewhat chopped about. The other is Mumble itself, which contains all the browser-specific classes. You also want packages.xml
The current versions are here: gtk-gui-0.13.tgz mumble-0.13.tgz packages.xml
Copy all files to a convenient location and unpack both packages. For convenience, create symlinks for the newly created directories.
If you copy an image file into this directory, you can now load and run Mumble from the Smalltalk prompt:
Having demonstrated that it works, you can save time by saving an image:
You can then start it in many ways. For example: