local file

I'm getting a local file via XMLHttpRequest in a C++ component.  In alpha 3
this worked.  In alpha 7 I crash in nsCrossSiteListenerProxy::OnStartRequest
with a NULL mRequestingURI.  The file is "resource:/config.xml" or
"file:///C:/alpha7/mozilla/bld/dist/bin/config.xml"   IsSameOrigin
fails-XMLHttpRequest sniffs out the chrome page that loaded the component
and  bypasses the NULL-principal thing  ("Until we got our principal story
straight we have to do this to support C++ callers")  So is this just
something I'm going to have to wait out or will I have to change the way I
do things?