The bug is related to the mozilla bugzilla bug: https://bugzilla.mozilla.org/show_bug.cgi?id=363447. With some investigation, I found that Java plugin might return uninitialized data to Firefox in file remotejni.cpp, in the functions jni_GetMethodID and jni_GetStaticMethodID, maybe more.

I think here is the problem: after the statement "retval = (jmethodID) checked_malloc(sizeof(struct _jmethodID));", the value "retval" should be set to zero.