No, Firefox (same as any of the big four) does not block ads or trackers by default. Brave does. We also have no-script and fingerprinting protection, currently opt-in by site (but we hope to engineer f.p. to on by default).
Blocking 3rd party ads and trackers really speeds things up!
IMHO Chrome has a better track record than Firefox when it comes to security issues, but Firefox has better privacy.