Hi Aside from dark themes that you can download from [https://addons.mozilla.org/en-GB/android/ here] or an add-on that might help (like one of [https://addons.mozilla.org/en-GB/android/search/?platform=linux&q=dark these]), to get a really good dark mode, I recomend that you try Firefox Preview from the Google Play store. It is an early look at what we are working on and may have one or two unresolved isses, but the dark theme is really good. Hope you like it.