I had a background image for the new tab page that has suddenly stopped working, it just displays a white screen. I clicked the 'reset to default' button next to 'Wallpapers' on the new tab page to try to fix the problem but nothing happens. No wallpapers show up under that section either where it used to be when it was working. I've restarted Firefox and the same thing happens. I have not enabled any third party CSS wallpaper.

Apart from that, everything else is working as it should. I'm sort of a computer-idiot so if anyone could please use layman's terms it would be very much appreciated!