I have LastPass setup with fingerprint reader, Firefox on Windows.
If I click the ... icon in a password field, Lastpass prompts me for Fingerprint as expected.
If I click the main Lastpass button in Firefox toolbar, then it prompts me for master password instead.
I went through all the troubleshooting steps of removing the extension and fingerprint setup, restarting, then reinstalling it.
PS. What is with this ridiculous "pick a label" prompt on the posting screen??
If you've already tried disabling and re-enabling fingerprint authentication and making sure the fingerprint reader is suppo..., we would recommend submitting a bug report following the steps here: https://support.logmeininc.com/lastpass/help/how-do-i-report-a-bug-to-lastpass