If an online Java application starts behaving unusually, it can be a good idea to clear the cache of temporary files that Java stores (you may want to do this in conjunction with clearing your browser's temporary files).
Launch System Preferences.
In the section labeled "Other" click on Java.
A separate window will launch. Under the section labeled "Temporary Internet Files" click on Settings...
In the window that appears, click on Delete Files...
Ensure that Trace and Log Filesand Cached Application and Appletsare checked, and then click OK.
When the small window disappears, the cache has been cleared.