No, stable. Oh, and they decided about:config is off-limits too for stable users.

I have both installed on this phone and that does not appear to be the case

Then you probably haven't been updated yet on stable. You can check r/firefox and everyone else there reports the same thing.

Maybe they're only rolling it out for some users. I got it too and it was updated through some kind of internal update manager, not through the app store. Deleted my browsing history as well.

Nightly has been this way for quite a while now.

Nightly for android is in the middle of some internal changes. Full add-on compatibility with post quantum add-ons will presumably return.