How about password protecting the entire user profile? Including fingerprint reader (unfortunately this function has been officially deactivated). Then you would first have to enter a password when starting FF, or scan your fingerprint.
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Hello@mumpel !This is definitely worth some consideration. Just want to highlight that in order to be secure user must lock their device and must protect their OS account. If attacker can get in OS account no Primary Password or fingerprint will be able to stop them.