From mouse movements

There are many tools, working through the Firefox browser, allowing the user to obtain printable paper wallets generating using the movements of the mouse as a source of entropy. Even if these tools are working in a web browser, they are written in javascript and are executed completely locally.

When these tools are started, they collect the movements of the mouse.

The entropy collecting phase

Then, when they have enough entropy, they provide a printable paper wallet.

The printable paper wallet, with keys and QR codes