<html:cancel > STRUTS -> InvalidCancelException

Front-end
#1

Bom dia, gostaria de uma ajuda com o código abaixo. Ao clicar no botão “Cancelar” no IE ele fecha a janela normalmente, mas no Firefox dá o seguinte erro:

javax.servlet.ServletException: org.apache.struts.action.InvalidCancelException
	org.apache.struts.chain.ComposableRequestProcessor.process(ComposableRequestProcessor.java:286)
	org.apache.struts.action.ActionServlet.process(ActionServlet.java:1913)
	org.apache.struts.action.ActionServlet.doPost(ActionServlet.java:462)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:710)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
	org.netbeans.modules.web.monitor.server.MonitorFilter.doFilter(MonitorFilter.java:390)

root cause

org.apache.struts.action.InvalidCancelException
	org.apache.struts.chain.commands.AbstractValidateActionForm.isCancelled(AbstractValidateActionForm.java:73)
	org.apache.struts.chain.commands.AbstractValidateActionForm.execute(AbstractValidateActionForm.java:111)
	org.apache.struts.chain.commands.ActionCommandBase.execute(ActionCommandBase.java:51)
	org.apache.commons.chain.impl.ChainBase.execute(ChainBase.java:190)
	org.apache.commons.chain.generic.LookupCommand.execute(LookupCommand.java:304)
	org.apache.commons.chain.impl.ChainBase.execute(ChainBase.java:190)
	org.apache.struts.chain.ComposableRequestProcessor.process(ComposableRequestProcessor.java:283)
	org.apache.struts.action.ActionServlet.process(ActionServlet.java:1913)
	org.apache.struts.action.ActionServlet.doPost(ActionServlet.java:462)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:710)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
	org.netbeans.modules.web.monitor.server.MonitorFilter.doFilter(MonitorFilter.java:390)

JSP

            &lt;html:submit value="Login" styleClass="botao"/&gt; | 
            &lt;html:cancel value="Cancelar" styleClass="botao" onclick="window.close()" /&gt;
#2