Conatinually asks to update plug-ins that are already updated?
You don't need to do anything since Java 7 Update 51 is not vulnerable (afaik) and is the recommended version offered at http://www.java.com/en/download/manual.jsp and http://www.java.com/en/download/
If you check the "[http://www.java.com/en/download/installed.jsp?detect=jre&try=1 Do I have Java?]" link at http://www.java.com/en/download/ and run the Java Detection applet it will tell you that you have the recommended Java installed (Version 7 Update 51).
*[https://bugzilla.mozilla.org/show_bug.cgi?id=985968 Bug 985968] - Mozilla Plugin check page displays Java plugin as vulnerable even if the latest version is installed.
*[https://bugzilla.mozilla.org/show_bug.cgi?id=985056 Bug 985056] - Java JDK 8 released
P.S. The bug reports are for information only. Don't comment in bug reports unless you have something constructive to add (see [https://bugzilla.mozilla.org/page.cgi?id=etiquette.html Bugzilla Etiquette]).