Its big thing originally was being a 64-bit port of Firefox. I assume it's still based on Firefox in some way, based on the name, but not really sure what it brings to the table anymore, besides some minor stuff you can already get with extensions.
Okay, hilarious. “Impressive that they’re keeping it up to date while maintaining XUL support”, I thought. Never mind.
Waterfox supports extensions that are no longer supported by Firefox.