The functionality isn’t enabled in Firefox for Android.

The justification is specifically that there’s no opt out available.

https://bugzilla.mozilla.org/show_bug.cgi?id=1909729#c5

Is this feature enabled on the mobile app?

I wouldn't call it a "feature" but I'm not sure. Their announcement didn't mention either way (that it was everywhere or desktop only)

The settings are present in about:config though (which is difficult to access on mobile also because they hide it).

Hopefully they will abandon this plan anyway due to all the criticism. It won't do any good unless google is on board anyway.