see last few comments in :  http://javafx-jira.kenai.com/browse/RT-27117
need to work with submitter in rt-27117 to find out how to reproduce the bug.
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Description: Upon completion of Java 7u10 installation, Firefox shows a message "A plugin is needed to display this content. Install Plugin"
 Steps to reproduce:
 1. Have a JRE and a standalone version of JavaFX installed
 2. Install Java 7u10 from Java.com
 3. Got to http://www.java.com/en/download/testjava.jsp to verify installation
 4. A message displays "A plugin is needed to display this content. Install Plugin"
 5. Proceed to install the plugin by clicking on "Install Plugin" 
Workaround: Uninstall standalone version(s) of JavaFX