If you're using any kind of third-party cookie (cookie TLD doesn't match URL TLD), then you will basically be reverting to a fallback cookie method. For example, metrics.example.com is your cookie domain www.example.org - since example.com and example.org are different TLD's, the cookie will be blocked, and Analytics falls back to a first-party cookie.
If you're using CNAME redirects (metrics.example.com on www.example.com), my research shows that neither Mozilla or Apple touches those cookies. If you're hosting the AppMeasurement JS file on your own domain (without Launch/DTM), then you even get through content blocked by private browsing.
If you're using the Experience Cloud ID service, those cookies aren't generally affected either since they are first party. They are currently blocked by private browsing, though, since Launch/DTM is currently on their list of tracking domains. Cross-site tracking capabilities are also disabled, since the ID service uses a demdex cookie to enable cross-site tracking (and that cookie is the prime target of both Mozilla and Apple).
I logged in to Analytics and ran a trended report over the past month for this forum's metrics with a Firefox-only segment, and none of the metrics I looked at were affected, not even by a tiny bit. The report suite I'm looking at uses the Experience Cloud ID service. The latest version should not affect any tracking, as long as there are measures in place to fall back to a first-party cookie. Cross-site tracking capabilities are absolutely affected, so unique visitors are not deduplicated across domains for Firefox/Safari users. This makes perfect sense, since that is Mozilla's/Apple's aim with these browsing features.
