The argument though is that it's not true E2E without the secure enclave. App data can be compromised in many ways. Apple goes to incredible lengths (including burning the root key which cannot be retrieved or reset from outside the enclave into the silicon during manufacturing with no way of them being able to tell what it is) to ensure a chain of trust from the point that anything physically enters the device.
In other words, with Firefox you trust the security of your device, whereas with Apple you trust the security of their entire ecosystem. In most cases, that's probably even a good thing, but I wouldn't exactly label one as strictly better than the other in all scenarios.
https://support.apple.com/en-us/HT212520
Although, I don't think that was accurate for iCloud Keychain anyway.
It's impossible to tell, though – Apple's platform security guide has been last updated in April 2022, which predates Advanced Data Protection. (Weirdly they do mention it in the document [1], though, so the date might also be incorrect and they might have added that information since I last looked a year ago.)
[1] https://help.apple.com/pdf/security/en_US/apple-platform-sec...
But iCloud access is forced to 2FA with one of your signed in devices, which requires the local password (pin, touch id, or face id, all of which never leave the enclave) to approve. There's really no way to get something covered by ADP short of physical device access + a stolen/coerced pin number.