java/icedtea-web and libxul

[Lena at lena.kiev.ua]

The last java/icedtea-web/Makefile update
http://www.freebsd.org/cgi/cvsweb.cgi/ports/java/icedtea-web/Makefile.diff?r1=1.24;r2=1.25;f=h
adds:

USE_GECKO=      libxul

What for?
I have www/firefox installed including /usr/local/lib/firefox/libxul.so .
Why do I need now to build and install also www/libxul port?