I have sync enabled on various desktop platforms (Win 7, Win 10), all using the same master password. My logins sync seamlessly across those browser. I have Firefox for Android set up on my phone, with sync properly configured, and no master password.

All of the other questions on mozilla support would lead me to believe that with this configuration, I should get passwords from my desktop browser sync'd to my phone. But this doesn't happen. Everything else seems to sync just fine, having just done a manual sync on both a desktop and then my phone.