Mullvad Browser Leaking Fingerprint

I have both stock Firefox and the Mullvad browser installed on my macbook. I visit fingerprint.com in both browsers to check how resistant by browser setup is to fingerprinting. On Firefox, when I purge cookies between visits, the fingerprint code changes, which suggests that as long as I purge cookies after visiting websites, I should be reasonable safe from fingerprinting. On the Mullvad browser (which by default is set up to not keep cookies, and which I have hardened further by choosing the strictest privacy settings), each time I visit fingerprint.com, the code is the same. I'm not sure what's wrong. How can a browser specifically made to improve privacy be less resistant to fingerprinting?