Accessing password vault on win10

A user has his windows 10 user account password protected and this user also uses the lastpass browser extension on Firefox which automatically signs the user in when Firefox is open.

The lastpass password vault can also be accessed offline with a locally cached version available but only if the computer is disconnected from the internet and the Firefox web browser is opened since auto login is enabled.

How difficult would it be to access the users password vault since the windows 10 machine is password protected?