I check this at: http://javatester.org/version.html
I already downloaded the latest SDK. It seems the issue is that
Java (TM) Platform SE 7 U5 10.5.1.255 has a warning that it has vulnerability and use with caution.
The thing is it's NOT disabled.
Also I already updated JDK to the latest version. I want to uninstall the plugin but there is no such option. I can only disable.
My other computer's firefox are doing fine.