При открытии странички с апплетом в консоли вижу:

$ firefox 

(/usr/lib64/firefox/plugin-container:2791): Gdk-WARNING **: The GDK_NATIVE_WINDOWS environment variable is not supported in GTK3.
See the documentation for gdk_window_ensure_native() on how to get native windows.
ERROR: ld.so: object 'libmozsandbox.so' from LD_PRELOAD cannot be preloaded (cannot open shared object file): ignored.
ERROR: ld.so: object 'libmozsandbox.so' from LD_PRELOAD cannot be preloaded (cannot open shared object file): ignored.
openjdk version "1.8.0_71"
OpenJDK Runtime Environment (build 1.8.0_71-b15)
OpenJDK 64-Bit Server VM (build 25.71-b15, mixed mode)

###!!! [Parent][MessageChannel::Call] Error: Channel error: cannot send/recv


###!!! [Parent][MessageChannel::Call] Error: (msgtype=0xA20006,name=PPluginInstance::Msg_NPP_SetWindow) Channel error: cannot send/recv