For years I've had an XAMPP local server set up in C: on my Win 7 machine. One of my local sites is a personal holiday database. Photos required for this are stored in D: as I can't clog up limted space on C: with them. They were accessed by using UNCs of the form "file:///d:/images/image.jpg"
Some time ago, that stopped working, apparently because of new default security settings in Firefox. The solution was to set 'security.fileuri.strict_origin_policy' to False instead of True. All was OK until very recently but now even that doesn't work, so it looks like something else has changed.
If anyone can shed any light on the situation then I'd be a happy bunny again - many thanks.