Native speaker here: yes, “primary” does not mean the same as “master”, and in this case I would argue that the distinction is relevant. I agree with your asse

Native speaker here: yes, “primary” does not mean the same as “master”, and in this case I would argue that the distinction is relevant. I agree with your assessment. “primary” — to me — implies one of many equally-important passwords. “master” implies a password that protects/overrides/controls all other passwords, which is what Thunderbird’s master password actually is.