Just about everything that uses xulrunner needs to load libgtkembedmoz.so, but the ebuild doesn't add /usr/lib/xulrunner/ to /etc/ld.so.conf.
you don't need this, firefox also does not add /usr/$(get_libdir)/mozilla-firefox to ld.so.conf what is this, which does not work?
Resolving INVALID per comment #1.