To the best of my knowledge, the only Apple devices with wide-gamut displays are the 2015 iMac and the 2016 9.7" iPad Pro. So I'd suspect that Firefox is either ignoring the color profiles, or handling them differently than Safari.
To be fair, on my 2013 rMPB, the Shoes one does not show a single difference whereas the Iceland, Italy, Sunset and Flower ones are much more vibrant and indicate that a wider gamut than sRGB may be available, but certainly not as much as the latest display.
