[Vinnl]

The encryption method is detailed here, that might potentially (not sure, as I don't know what KDF is) answer your question: https://hacks.mozilla.org/2018/11/firefox-sync-privacy/

But encryption does depend on your password:

> The crux of the difference in how we designed Firefox Accounts, and Firefox Sync (our underlying syncing service), is that you never send us your passphrase. We transform your passphrase on your computer into two different, unrelated values. With one value, you cannot derive the other. We send an authentication token, derived from your passphrase, to the server as the password-equivalent. And the encryption key derived from your passphrase never leaves your computer.

[yellow_lead]

Thanks! KDF is key derivation function. Looks like they are using PBKDF2.