nsIFileURL is now frozen. see http://bugzilla.mozilla.org/show_bug.cgi?id=157135 for details. no changes were made to the interface before freezing.
on the implementation side, nsStandardURL (the main implementation of nsIFileURL in the mozilla codebase) was modified to make support for nsIFileURL conditional at time of construction. nsStandardURL defaults to not supporting nsIFileURL. this is consistent with the old implementation. now, only the file:// and resource:// protocol handlers generate nsIURIs that are QI'able to nsIFileURL. (http, https, and ftp used to generate nsIURIs capable of being QI'd to nsIFileURL, which made no sense!) darin
