firefox.exe hung on Vista (build 5384) when running our 5.0 Update 7 JRE. I have pasted the stack below and the complete windows dump can be found at http://javaweb.sfbay/~gmanwani/ms-cabs/jvm-busyhang/0298397590.cab

ntdll!KiFastSystemCallRet
ntdll!NtWaitForSingleObject+0xc
kernel32!WaitForSingleObjectEx+0xfa
kernel32!WaitForSingleObject+0x12
jvm!ObjectMonitor::enter(class Thread * __the_thread__ = 0x00000001)+0x199 [C:/BUILD_AREA/jdk1.5.0_07/hotspot\src\os\win32\vm\objectMonitor_win32.cpp @ 180]
jvm!ObjectSynchronizer::slow_enter(class Handle obj = class Handle, class BasicLock * lock = 0x0012dd0c, class Thread * __the_thread__ = 0x05512e08)+0x117 [C:/BUILD_AREA/jdk1.5.0_07/hotspot\src\share\vm\runtime\synchronizer.cpp @ 374]
jvm!InterpreterRuntime::monitorenter(class JavaThread * thread = 0x05512e08, class BasicObjectLock * elem = 0x0012dd0c)+0x52 [C:/BUILD_AREA/jdk1.5.0_07/hotspot\src\share\vm\interpreter\interpreterRuntime.cpp @ 487]
WARNING: Frame IP not in any known module. Following frames may be wrong.
0x759e440
jvm!JavaCalls::call_helper(class JavaValue * result = 0x2333a8d8, class methodHandle * m = 0x00000001, class JavaCallArguments * args = 0x00000000, class Thread * __the_thread__ = 0x0012dd80)+0x12b [C:/BUILD_AREA/jdk1.5.0_07/hotspot\src\share\vm\runtime\javaCalls.cpp @ 378]
jvm!os::os_exception_wrapper(<function> * f = 0x6d7462d6, class JavaValue * value = 0x0012dff4, class methodHandle * method = 0x0012df04, class JavaCallArguments * args = 0x0012df44, class Thread * thread = 0x05512e08)+0x5e [C:/BUILD_AREA/jdk1.5.0_07/hotspot\src\os_cpu\win32_i486\vm\os_win32_i486.cpp @ 55]
jvm!JavaCalls::call(class JavaValue * result = 0x6d74b68d, class methodHandle method = class methodHandle, class JavaCallArguments * args = 0x0012dff4, class Thread * __the_thread__ = 0x037ea0cc)+0x1b [C:/BUILD_AREA/jdk1.5.0_07/hotspot\src\share\vm\runtime\javaCalls.cpp @ 281]
jvm!jni_invoke_nonstatic(struct JNIEnv_ * env = 0x05512ec8, class JavaValue * result = 0x0012dff4, class _jobject * receiver = 0x037ea0cc, JNICallType call_type = JNI_VIRTUAL (1), struct _jmethodID * method_id = 0x055ce9d0, class JNI_ArgumentPusher * args = 0x0012dfd8, class Thread * __the_thread__ = 0x04ec4e48)+0x147 [C:/BUILD_AREA/jdk1.5.0_07/hotspot\src\share\vm\prims\jni.cpp @ 869]
jvm!jni_CallVoidMethodV(struct JNIEnv_ * env = 0x05512ec8, class _jobject * obj = 0x037ea0cc, struct _jmethodID * methodID = 0x055ce9d0, char * args = 0x0012e02c "???")+0x4b [C:/BUILD_AREA/jdk1.5.0_07/hotspot\src\share\vm\prims\jni.cpp @ 1082]
jpinscp!JNIEnv_::CallVoidMethod+0x1a [C:/BUILD_AREA/jdk1.5.0_07/control/build/windows-i586/include\jni.h @ 1024]
jpinscp!JavaPluginObject::stopPlugin+0x5d [../../../../src/plugin/win32/nscore/JavaPluginObject.cpp @ 287]
jpinscp!CJavaPlugin::Stop+0x2b [../../../../src/plugin/win32/nscore/CJavaPlugin.cpp @ 482]
jpioji!CNSAdapter_JavaPlugin::Stop+0x1a [../../../../src/plugin/share/adapter/common/CNSAdapter_JavaPlugin.cpp @ 187]
firefox!nsPrintSession::Init+0x6965
firefox!nsRegionRectIterator::operator=+0x32f68
firefox!nsRegionRectIterator::operator=+0x32f68