The android version of firefox should follow the "system" for its auto dark mode instead of following the "battery saver". Just like chrome and other chromium browsers do.
The major advantage this gives is that it allows even older android version users to experience auto dark mode, since there are ways for them to initiate system wide dark mode through 3rd party apps (like this one for example: https://play.google.com/store/apps/details?id=systems.maju.darkmode&hl=en&gl=US)
But since Firefox follows battery saver, this never works on android version lower than 10.
Therefore, I'd like to request the developers to implement the auto dark mode in firefox android to follow the system instead of the battery saver status.