Isn't that just what has to be selected in the play store to allow the app to access/use the localization framework in Android? It doesn't guarantee they're sharing information. They could still do it on a site by site bases with in-app approvals?
I guess the concept has gone from "We don't support this at all" to "We support it but won't be evil, you have to trust us."
How much do we trust Mozilla/Firefox? You could always go read the code yourself: https://hg.mozilla.org/mozilla-central or just do what most people do and hope someone else audits it :)
There's a choice between first party(collected) and third party(shared). Also a list of purposes one chooses from. This could include "App functionality", "Analytics", "Account management", etc...
Two of the possible 3rd party choices are "Advertising or marketing" and "Personalization". These two have been chosen for firefox. This includes sharing data with advertising partners.
A change to those options is what triggered the notification. It's not a requirement for using location features.
I'd say a part of figuring out what they are doing is reading such information. Even if the code itself doesn't reflect it yet, it's usually listed in preparation.
It's also a good way to figure out the code needs to be reviewed :)
Opening the "data safety" section another pop-up[1] comes up and the specific use-cases listed are "advertising or marketing" and "personalisation".
[1] - https://i.imgur.com/QwqiQna.jpeg