I am using today's nightly version of JBoss Tools but the HTML Editor is not working, probably due to the change to XULRunner or at least it seems. Every time I try to open an XHTML file the following error appears and nothing is displayed, not even the source editor.

Could not open the Visual Page Editor: No more handles [Could not detect registered XULRunner to use]
No more handles [Could not detect registered XULRunner to use]

The log shows an exception:

Unable to create editor ID org.jboss.tools.jst.jsp.jspeditor.HTMLTextEditor: An unexpected exception was thrown.
java.lang.NullPointerException
at org.jboss.tools.vpe.editor.mozilla.MozillaEditor.getEditor(MozillaEditor.java:1049)
at org.jboss.tools.vpe.editor.VpeEditorPart.createVisualEditor(VpeEditorPart.java:916)
at org.jboss.tools.jst.jsp.jspeditor.JSPMultiPageEditor.pageChange(JSPMultiPageEditor.java:211)
at org.jboss.tools.jst.jsp.jspeditor.JSPMultiPageEditor.createPages(JSPMultiPageEditor.java:407)
at org.jboss.tools.jst.jsp.jspeditor.JSPMultiPageEditorPart.createPartControl(JSPMultiPageEditorPart.java:125)
at org.eclipse.ui.internal.EditorReference.createPartHelper(EditorReference.java:662)
at org.eclipse.ui.internal.EditorReference.createPart(EditorReference.java:462)
at org.eclipse.ui.internal.WorkbenchPartReference.getPart(WorkbenchPartReference.java:595)
at org.eclipse.ui.internal.EditorReference.getEditor(EditorReference.java:286)
at org.eclipse.ui.internal.EditorManager.findEditor(EditorManager.java:403)
at org.eclipse.ui.internal.WorkbenchPage.busyOpenEditorBatched(WorkbenchPage.java:2799)
at org.eclipse.ui.internal.WorkbenchPage.busyOpenEditor(WorkbenchPage.java:2762)
at org.eclipse.ui.internal.WorkbenchPage.access$11(WorkbenchPage.java:2754)
at org.eclipse.ui.internal.WorkbenchPage$10.run(WorkbenchPage.java:2705)
at org.eclipse.swt.custom.BusyIndicator.showWhile(BusyIndicator.java:70)
at org.eclipse.ui.internal.WorkbenchPage.openEditor(WorkbenchPage.java:2701)
at org.eclipse.ui.internal.WorkbenchPage.openEditor(WorkbenchPage.java:2685)
at org.eclipse.ui.internal.WorkbenchPage.openEditor(WorkbenchPage.java:2676)
at org.eclipse.ui.ide.IDE.openEditor(IDE.java:651)
at org.eclipse.ui.ide.IDE.openEditor(IDE.java:610)
at org.eclipse.jdt.internal.ui.javaeditor.EditorUtility.openInEditor(EditorUtility.java:361)
at org.eclipse.jdt.internal.ui.javaeditor.EditorUtility.openInEditor(EditorUtility.java:168)
at org.eclipse.jdt.ui.actions.OpenAction.run(OpenAction.java:229)
at org.eclipse.jdt.ui.actions.OpenAction.run(OpenAction.java:208)
at org.eclipse.jdt.ui.actions.SelectionDispatchAction.dispatchRun(SelectionDispatchAction.java:274)
at org.eclipse.jdt.ui.actions.SelectionDispatchAction.run(SelectionDispatchAction.java:250)
at org.eclipse.jdt.internal.ui.navigator.OpenAndExpand.run(OpenAndExpand.java:49)
at org.eclipse.ui.actions.RetargetAction.run(RetargetAction.java:221)
at org.eclipse.ui.navigator.CommonNavigatorManager$3.open(CommonNavigatorManager.java:202)
at org.eclipse.ui.OpenAndLinkWithEditorHelper$InternalListener.open(OpenAndLinkWithEditorHelper.java:48)
at org.eclipse.jface.viewers.StructuredViewer$2.run(StructuredViewer.java:842)
at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
at org.eclipse.core.runtime.Platform.run(Platform.java:888)
at org.eclipse.ui.internal.JFaceUtil$1.run(JFaceUtil.java:48)
at org.eclipse.jface.util.SafeRunnable.run(SafeRunnable.java:175)
at org.eclipse.jface.viewers.StructuredViewer.fireOpen(StructuredViewer.java:840)
at org.eclipse.jface.viewers.StructuredViewer.handleOpen(StructuredViewer.java:1101)
at org.eclipse.ui.navigator.CommonViewer.handleOpen(CommonViewer.java:467)
at org.eclipse.jface.viewers.StructuredViewer$6.handleOpen(StructuredViewer.java:1205)
at org.eclipse.jface.util.OpenStrategy.fireOpenEvent(OpenStrategy.java:264)
at org.eclipse.jface.util.OpenStrategy.access$2(OpenStrategy.java:258)
at org.eclipse.jface.util.OpenStrategy$1.handleEvent(OpenStrategy.java:298)
at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:84)
at org.eclipse.swt.widgets.Display.sendEvent(Display.java:3543)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1250)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1273)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1258)
at org.eclipse.swt.widgets.Widget.notifyListeners(Widget.java:1079)
at org.eclipse.swt.widgets.Display.runDeferredEvents(Display.java:3441)
at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3100)
at org.eclipse.ui.internal.Workbench.runEventLoop(Workbench.java:2405)
at org.eclipse.ui.internal.Workbench.runUI(Workbench.java:2369)
at org.eclipse.ui.internal.Workbench.access$4(Workbench.java:2221)
at org.eclipse.ui.internal.Workbench$5.run(Workbench.java:500)
at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:332)
at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:493)
at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:149)
at org.eclipse.ui.internal.ide.application.IDEApplication.start(IDEApplication.java:113)
at org.eclipse.equinox.internal.app.EclipseAppHandle.run(EclipseAppHandle.java:194)
at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.runApplication(EclipseAppLauncher.java:110)
at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.start(EclipseAppLauncher.java:79)
at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:368)
at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:179)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:559)
at org.eclipse.equinox.launcher.Main.basicRun(Main.java:514)
at org.eclipse.equinox.launcher.Main.run(Main.java:1311)