Nick wasn't seeing the forest for trees when he wrote that comment - Denis did an attempt on a proper fix - if you have time try use the nightly update site and let us know if it works (http://download.jboss.org/jbosstools/updates/nightly/trunk/)
About Xulrunner then the problem is that there is an actual XulRunner 64 bit binary but not a 64 bit SWT/XulRunner binding library.
And yes, this does not paint a good picture for the future usage of xulrunner.