Impressive. Vivaldi (which is a fork of a Chrome) gives me a score of a 97 so on a certain level SerenityOS' web browser is better than a chrome fork.
As far as I know the standards have changed in some regards, the browsers have been updated to reflect those changes but the Acid 3 test suite has not and therefore some tests fail under the current interpretation of the tested web standards.
That's amusing. Firefox 97.0 (on my machine) has a score of 97 as well.