Relay uses a username flow so bookmark sync does not need an email identity as its foundation.
What Relay asks for instead
The password saved in your Recovery Kit works in every supported client. Compatible Chromium browsers can also add an optional passkey; Firefox does not use passkeys in its first release.
The extension needs bookmark access to read, compare, preserve folders, and apply changes in the browser.
Relay keeps local browser identity, session state, plan cache, and sync metadata in browser storage.
Compare the tradeoff: Read the privacy policy or choose your browser.