[jruderman]

Fennec doesn't use XUL for primary UI, but it's still compiled with XUL enabled.

Fennec's improved launch speed is partly due to the order in which components are loaded: the primary UI can appear before the layout engine is ready.

Compiling without XUL would shave some size off the binary, but probably not a whole lot. Most of the code involved in rendering XUL is the same code that renders HTML.