Toggley от Farid Zelli

A simple button that toggles between Firefox's default Light and Dark themes. To use it, simply tap or click on the icon to switch themes.

Toggley works best with Dark Reader.
The default keyboard shortcut is Ctrl+Shift+0.
See Manage extension shortcuts in Firefox for more info.

Experiencing a problem? Make sure that:
1. Website appearance is set to "Automatic" in settings
2. privacy.resistFingerprinting is set to "false" in about:config
3. "Use system color scheme" and "Detect dark theme" are enabled in Dark Reader

This lightweight add-on is fully open-source.