WM_COPY trouble

[mozilla.dev.extension]

i created an extension, which is protocol handler.
inside extension, i create window (with WinApi) that will catch WM_COPY
msg,
then i launch an app, and SendMessage(WM_COPY) to it;
when app processed data, it replies SendMessage(WM_COPY) to me
and in this place it holds inside SendMessage
i think the cause of it is Mozilla don't process Windows messages
so i tried to create thread with message pump, but it not work
Code:

{
printf("thread is running");
...
MSG msg;
while (PeekMessage(&msg, NULL, 0, 0, PM_REMOVE))
{
printf("run peek\r\n");
TranslateMessage(&msg);
DispatchMessage(&msg);
}
...
}

so' i newer seen 'run peek' in debug window, i only seen "thread
running"

does anybody know, what i need to do for normal message processing ?

[mozilla.dev.extension]

WM_COPYDATA of course