My guess is that it's a problem with
the xulrunner on ubuntu. Please try the snippet below (you may need
to change its GRE_LOCATION value). The only swt it uses is the OS
class to invoke a few gtk functions. All xulrunner interactions are
done via JavaXPCOM, so you'll need MozillaInterfaces.java from http://releases.mozilla.org/pub/mozilla.org/xulrunner/releases/22.214.171.124/contrib/sdk/xulrunner-126.96.36.199.en-US.linux-i686.sdk.tar.gz
on your project's build path. It your xulrunner is answering these
values properly then two alerts should be printed to stdout.