Brave randomizes the output of fingerprinting techniques like canvas rendering, system fonts, installed devices, etc in a way that makes you look like a real, consistent user providing real data that still allows the site to work, while still changing the output from one session to the next enough that sites can't tell you're the same person.

Firefox claims to block all this but if you check their site they explain how it actually works:

Firefox protects users against fingerprinting by blocking all third-party requests to companies that are known to participate in fingerprinting

We’ve partnered with Disconnect to provide this protection. Disconnect maintains a list of companies that participate in cross-site tracking, as well a list as those that fingerprint users.

This does nothing to actually disguise you. It's the equivalent of putting a paper bag over your head when you think there's a security camera. You stand out because of the bag and you don't know where all the cameras are so you're still being tracked when you don't know it.

I hate the idea of Brave because Chromium's dominance will ruin the web but Firefox does not protect us.