Download UltimaDark - The Fastest Dark Mode Extension for Firefox. UltimaDark uses agressive & smart techniques to turn even the sunniest websites into realms of darkness.
Although it works well, this is so experimental, it makes lab rats look like seasoned professionals.
Go ahead, embrace the ...
Nope, you can install extensions to regular FF for a while on Android. Go to addons.mozilla.org and install like how you would do it on desktop. Request desktop site if extension claims to be incompatible.