Beta & Nightly indicate different versions of the one app

Preview on the other hand is the name of a 100% different app (new codebase): it is intended to eventually replace the legacy Firefox app

Transitions/migrations can be confusing times

It's trendy now to have multiple listings for your browser. See other examples:

Opera (5): https://play.google.com/store/search?q=opera&c=apps&hl=en_US

Chrome (4): https://play.google.com/store/search?q=chrome&c=apps&hl=en_U...

You did not mention Firefox Focus!

It'll be simpler once the switch to the rewrite (currently called "Firefox Preview") is done. Then presumably we'll just have:

"Firefox" / "Firefox beta" / "Firefox nightly for developers"

"Firefox Focus"

The private windows in Firefox Preview behaves exactly like Firefox Focus. You can open links by default in a private window in settings.

I'm not sure if this means that Focus will be deprecated in favour of Preview, or will it remain a stripped down version of Preview.

Exactly like?

I'm under the impression Firefox Focus on Android uses the native (Chrome) renderer, not the the Gecko engine.

That was accurate until Focus v6. Since then, Focus switched to GeckoView, which is somehow different than Gecko, though I don't know how.

It goes Stable -> Beta -> Nightly in terms of closeness to trunk. I believe Preview == Beta and Preview Nightly == Nightly now. The Preview apps are going away since the new interface is releasing soon

Now I am even more confused

IIRC, the two "preview" ones are the new Firefox, the other three are the long-existing Firefox. So once the new Firefox replaces the old, the two "preview" apps won't be necessary anymore.