"No shady privacy policies or back doors for advertisers" proclaims the Firefox homepage, but that's no longer true in Firefox 128.
Less than a month after acquiring the AdTech company Anonym, Mozilla has added special software co-authored by Meta and built for the advertising industry directly to the latest release
All your data is encrypted on our servers so we can’t read it – only you can access it. We don’t sell your info to advertisers because that would go against our data privacy promise.
You are correct. My mistake.
https://www.mozilla.org/en-US/firefox/features/sync/