hebig.org/blog

From the release note: "Version 0.50 has finally been released. It's a major evolution from version 0.40 which was a re-write from the original. In particular, it includes support for the full set of XUL elements, attributes and attribute values [and] includes simultaneous graphic and text views of a XUL Document."

Note that this visual XUL editor comes with a lot of user documentation that might also serve as a good starting point if you want to learn about XUL.

Go and get it