If it aint broke, don't fix it, and mull works very well. While it's nice to see alts becoming more widely available, it's still mull or bust in my book!

Firefox Focus is an Android browser that's always in Private Browsing mode, and has tracker blocking and content blocking built-in. It does not have all of the advanced features of the regular Firefox app.

Firefox Nightly is the cutting-edge development version of Firefox. This is built from the latest codebase automatically on a nightly base, as the name implies. If you want the newest features ASAP and don't care about bugs or stability issues, this is the one for you. Personally I would recommend using Firefox Beta instead, which sits in the middle -- more tested than Nightly, more cutting-edge than regular Firefox.

Firefox Klar is the German-language version of Firefox Focus. I think the only technical difference is that it has telemetry disabled by default. (You can turn that off in Firefox Focus as well, under Settings > Privacy & Security).

Never heard of Iceraven before. Apparently it's a fork of Mozilla's development version of a new Android app codenamed Fenix. Hopefully someone else can chime in with more insight into these two.

If Firefox focus Android has user-friendly tab management, it'll be my main browser. Its native ad blocker is 👍. 1 may say that there's Firefox Android + Ublock origin. But I <3 Firefox and I'm :) they have a native ad blocker.

Firefox focus also has the epic feature of not being able to add new bookmarks for some goddamn reason and also needing to close the app if the webpage doesn’t let you scroll up.