FF8 seem to perform brute force detection of java plugin based on list of Java Runtimes installed in addition to traditional way to register plugins.

This result in 2 java plugins - one from "latest full JRE" on the system and another from JavaFX Runtime.
Moreover, JRE plugin has a preference!

As a result JavaFX applications do not work in FF8 until user manually disables "JRE" version of plugin in the Tools->Add Ons->Plugin
unless they have installed JRE7u2. We do attempt to start application as JavaFX runtime as JavaFX is detected by DT.

With 6u29 situation is worse as we also get second copy of DT plugin registered for the same reason. So, we complain JavaFX is not installed although it is.

Summary of UE for 2.0.2 and different versions of JRE installed:
   1) 7u2 => works (although using plugin from 7u2)
   2) 7u1 or 7 => FAIL. complain on "system misconfig" as JRE7 plugin is not compatible with latest FX runtime.
   3) 6u29 => FAIL. Report "No JavaFX installed" as old DT plugin is used.

Workarounds:
   a) Do not use FF8 (other browsers and other versions of FF are ok)
   b) After JavaFX is installed go to Tools->Addons in FF8 and
       make sure only ONE version of Java (TM) Platfrom is enabled (with largest version string, 10.2.1 for FX 2.0.2)
       and only one version of Java Deployment Toolkit (should be version 10.2.*)

Fix:
   At this point it is unclear what can be done in FX installer to avoid this issue besides renaming new_plugin directory in all installed versions of JRE.
Need to contact FF to find out if they can revert brute force behavior shortly.