I am using 64bit version of eclipse running in 64 bit jdk and therefore cannot use the visual page editor (and its embeeded JBoss Tools Mobile Browser Simulator)
According to https://community.jboss.org/thread/164805 the root problem insists of using XUL-Runner which is not supported in 64 bit.
Maybe, I am getting it technicially wrong, but why not replacing XUL-Runner by using an integrated webkit-runtime whitin the jboss tools.
With an integrated webkit, visual page editor can be used in 64 bit mode.
By the way, I am not sure, if this is correct, but http://wiki.mozilla-x86-64.com/Download contains a file "xulrunner-10.0.10.en-US.win64-x86_64.zip" which seems to be a 64-bit version of XUL-Runner.