User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14_5) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/12.1.1 Safari/605.1.15

Steps to reproduce:

I've been experimenting with CSS that adapts to the preferred color scheme of the user and noticed while testing Safaris devtools that they include a useful toggle for "dark mode" that let me quickly test the opposite color scheme without changing the system settings. The toggle is available in the Elements pane (their Inspector) in the same area as their print style toggle.

Actual results:

I tried looking for something similar in Nightly, but couldn't find it in the Inspector pane or in settings. I tried searching for related issues and didn't find anything on the topic.

Expected results:

I would love to see this feature in the Inspector pane in Firefox.

Is this a feature you would consider now that Firefox supports prefers-color-scheme? Perhaps a toggle could fit next to the print media simulation toggle, similar to Safari?

Thanks for the report. We already have this feature request on file, so I will close this one as duplicate.