I really love the Dark Reader Browser plugin (h/t Chris Erin). It turns most websites into a dark mode that is really easy on my eyes. However, some sites just don't look right in dark mode. Luckily, the plugin can be toggled on and off with
ALT + SHIFT + D on Firefox and Chrome. I use it a couple of times a day on websites I encounter on the internet.
Bonus: Here's an example of this plugin in action, that is very meta.