如果测试用例失败，Selenium Web驱动程序无法关闭firefox实例

i folks, i am using junit with selenium web driver 2.28. the problem is if i run a successful test case the web drives is able to close the firefox instance, but when a test case fails the selenium web driver is not able to close the firefox. i am using FF 15.0.1 with selenium-server-standalone-2.28.0.jar. please respond thanks Sahili folks, i am using junit with selenium web dri