Neither Masterpassword nor it's authors collect any information from or about the usage of Masterpassword, period.

Masterpassword store your settings (site name, etc) locally on your device. This information is never transferred anywhere by Masterpassword.

Your browser vendor may collect data on your usage. Please refer to your vendor's policy for details. Further, if you have enabled synchronisation of addon-settings within your browser, the browser may transfer and store this on a synchronisation server. Again please refer to your browser vendor's policy for details.

The "Sync Site Data" setting in this addon will allow the browser to sync your settings (site name, user name). Note that the password or master key is never transferred.