FYI, OS X has the same problem with the 64 bits version of Eclipse. Installing the Jboss tools visual editor (which for some reason appears under the name "richfaces"(?) on the update site) fails because of the dreaded XULRunner dependency. Installing the 32 bits version of Eclipse solves the problem.
Would it be possible to make the XR dependency optional?
p.s.
On 64 bits Ubuntu 10.04 it just works.