Java applets don't work in FFP, but Java Script does

Hi,
can anyone help me with my problem:

-> test on java.com: script works, but applet remains blank.
however, both work fine on the non-portable Firefox and IE, so the JAVA installation seems to be OK

Settings:
- FFP 3.5.2 on Windows XP SP3
- JAVA RE 6.15 installed (not Portable JAVA)
- JAVA Settings: Default Java for browsers/Mozilly Family -> enabled
- FFP Settings: Java Script/Java -> enabled; No-Script/Ad-Block -> disabled for java.com
- npdeploytk.dll and npjp2.dll in plugin directory

thanks