XUL Explorer is described as 'Lightweight XUL IDE, built as a XULRunner application that provides an easy way to experiment with XUL. It’s a simple editor that can preview XUL inline or in a separate popup window. It has a list of code snippets (small fragments of XUL or JavaScript) that' and is an app. There are 2 alternatives to XUL Explorer for Mac, Windows, Linux and Eclipse. The best XUL Explorer alternative is XUL Gear, which is both free and Open Source.
XUL Gear is a powerful and easy to use extension that plays the role of an XUL editor. XUL Gear allows Firefox developers to write less xml code and to arrange XUL objects in a visual form ( in the WYSIWYG manner).
XulBooster is an Eclipse Feature adding XUL support to the Eclipse IDE and WTP. The Feature includes Editors, Views, Wizards, Snippets, Help, Builder etc. you can develop with it firefox extension, xulrunner application for example.
