This prevents cross-file access from files loaded into the browser from
the local file system, further restricting the origin policy of file:
URIs.
Added a pref to control this behavior for local file access if required
for certain applications, since this change might break using the
browser to run applications on the local file system that require
access to local files.
This creates a number of stubs and leaves some surrounding code that may be irrelevant (eg. recorded time stamps, status variables).
Stub resolution/removal should be a follow-up to this.
