Wikipedia
KaXUL (KDE Advanced XUL) is a reimplemetation of Mozilla's own XUL framework for KDE. Written by George Staikos, it allows for XUL applications - both client- and server-side - to be read by native Qt widgets. uXUL ( UI XUL), also made by Staikos, takes a XUL application, uses KaXUL to convert it, and then run it as a native KDE plugin. Used together, one can access XUL applications using Konqueror or any other Web browser using the KHTML layout engine. Previously, XUL applications were only used by browsers using the Gecko layout engine, which is used, most famously, by Mozilla Firefox for the generation of its extensions.
It was first released by Staikos in 2003, but no update has occurred to KaXUL since then. It still remains downloadable as of November 2006, but was never integrated into official Konqueror or KDE development for fears of code bloat.