For an unknown (yet) reason, Maven tests using VPE need to set the "org.eclipse.swt.browser.XULRunnerPath" system property to a platform-specific value. This requires people on other platform to tweak the pom for their specific environment, which is not convenient.
VPE should behave like Eclipse browser to resolve XulRunner, which runs well with Maven: http://www.eclipse.org/swt/faq.php#howdetectmozilla . Seems like there is a difference somewhere that makes VPE fail where SWT Browser works.
An example project is jsf/tests/org.jboss.tools.jsf.ui.bot.test