A good point. Firefox sync has zero-knowledge encryption, Chrome sync doesn't. It is just that if Firefox sync stores your history, Chrome sync probably does it too.
And interestingly, you could have a page showing your search history with Firefox sync just like with Google. Just because a page shows you private data doesn't mean someone else has access to it, and the more common opposite is also true.
Not exactly zero-knowledge, just end-to-end. They have the encryption key (called kB), but it's encrypted with a key derived from your password.
(Note, that while the password and key derived from it never normally leave the brwser, the login page is served from the network. So, you trust Mozilla's servers to not get hacked and serve you insecure login page.)
The system also has a notion of "class A" storage, where Mozilla knows the key (called kA), but AFAIK nothing ever used that. Maybe its already gone.
Oh, the device names (and types - like desktop vs android) are not encrypted. Probably because of attempts to add push updates (normally, sync is just polling for updates). And the profile data too (not a part of Sync at all - its Accounts).
Google has optional client-side (also, E2E) encryption, for some types of the data (e.g. passwords and autofill data). One has to opt in explicitly. When opted in, data is encrypted with a key that's is derived form a passphrase you provide (and sync implementations would error and ask you for the passphrase). I'm not sure, but IIRC protocol has provisions that allow to not encrypt some data at client's (= Chrome's) discretion, as the encrypted flag is set per-object. I'm not aware if this is used or not - was a very long while since I've looked at their sync server implementation.
That said, for E2E encryption both system have feature parity, but Mozilla's one has it by design and Google's one only as an opt-in.
And interestingly, you could have a page showing your search history with Firefox sync just like with Google. Just because a page shows you private data doesn't mean someone else has access to it, and the more common opposite is also true.