In the debug dev tools inspector window, there are buttons to preview how the website looks with certain "prefers-color-scheme" settings enabled. I propose the addition of a button to preview the site with "prefers-reduced-motion" as toggling this setting on and off in firefox's "about:config" page isn't immediately obvious and not as fast.
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Yes, agreed, this would be nice addition to the existing support for color scheme
According to this MDN page
...there is ui.prefersReducedMotion that can be set to either 0 for full animation or to 1 to indicate a preference for reduced motion.
I filed the following bug, so this idea isn't lost