Firefox color management settings break Windy display
I tracked down the setting causing Windy to display like this in Forecast Fox as well as on the main website. If the color management is set other than default (gfx.color_management.mode) it displays like in the image here.
On further investigation, it's an issue with forcing browser color management on images that don't have an imbedded color profile. This is something important on wide-gamut monitors so colors don't look garishly bright and saturated.
Setting Firefox to manage all images (even when they don't have a profile embedded) creates this problem with Windy.com.