The JFBCSystem plugin is actually new to the 3.0.2 release. We haven't called it out on the Overview page yet to ensure that everyone enables it. We'll be adding more features to it in future releases, but for now, it only has a fix for some module issues that some sites experience when viewed in Internet Explorer. It's definitely best to have it enabled, but it isn't necessarily required.
Hope that helps clear up some confusion.
upgrading to 3.0.2 plugin disable itself
that's all