On the privacytest.org website, Firefox’s privacy protection capabilities are not as good as those of Brave and Librewolf.Such as,Cross-session first-party tracking tests and Cross-session third-party tracking tests and Tracker content blocking tests . I suggest you improve your privacy protection based on the test results of this website and strive to pass all test items. Improve your privacy protection beyond Brave and Librewolf browsers
In order to remain able to produce an experience that is comparable to other major browsers, they are going to ignore most of that. Doesn't stop you from using about:config or a user.js file to set up your browser that way but expect some breakage here and there in terms of expected website performance, featureful JS web applications and maximum privacy are at times incompatible, not saying that's good or bad its just how it is.
Librewolf is pretty good though and according to that list is the star student. Note though, there are numerous (dozens or more) factors that are not being addressed by that list in terms of privacy alone. That is hardly comprehensive on top of leaving out how perfectly secured browsers in privacy terms can't really access the modern web. Optimal privacy involves turning off JS which breaks 90%+ of the web, so keep that in mind.
Also if using Windows and to some degree macOS, even worrying about Firefox's privacy profile is being "penny wise, pound stupid" since the OS is already going to compromise your privacy regardless of your browser at more fundamental levels so the company that makes it can sell your data to advertisers and make even more money than the amount you paid to use their OS.