Spring Webflow FlowScope gets empty

I'm working on CAS server, and it is highly required that if we have more than three failed login attempts, for fourth time there has to be captcha. In order to accomplish this process, I have used

context.getFlowScope().put("count", count);

in which, the count variable counts the number of failed attempts. with Google Chrome it works fine, but with Mozilla FireFox, after second attempt, surprisingly the count variable gets zero again.