Bug RT-21321 haven't been fixed completely.
It can be reproduced on firefox only with other test cases, such as http://sqeweb.us.oracle.com/deployment2/sheldon/webCases/javafx/liveconnectfx/html/testJStoJavafx_Call_OverloadedMethod_String_Arg.html

Steps to reproduce:
1) Install 7u6 b23
2) load applet http://sqeweb.us.oracle.com/deployment2/sheldon/webCases/javafx/liveconnectfx/html/testJStoJavafx_Call_OverloadedMethod_String_Arg.html
3) if no "TEST FAILED" or "TEST PASSED" is printed in console, bug is reproduced.
if close the browser and launch the applet again without cleaning deployment cache, it works well.

Note: IE works fine.