@denschub I think one of the issues here is that default Firefox is not primarily aimed at the "hard privacy" users who do not use default settings and routinely block all ads and trackers.
To kill online advertising would require killing the ad supported sites and servers, which is in fact something I consider a desirable goal. Then we get back to self-hosting and now distributed hosting, which are far safer and more private.
Until then, the default user who uses websites that attempt to block those who block ads and uses ad supported streaming services cannot use a hard privacy browser because such things as video on news sites much less the DRM shit like Hulu and Netflix are very heavily armored.
I've already seen websites whine about enhanced tracking protection, the real problem is too few users willing to boycott such websites, to close their accounts with ad supported services.
Mozilla allows users to turn this one off with a single checkbox, same as turning off playing DRM content and thus downloading a closed source decryptor for such contents.
For my use, I always assume any browser update could contain what on my end of the spectrum are antifeatures. Thus the first run is always done disconnected from the Internet. This lets me find and disable problematic features. I make much use of about:config to deal with things that are not in the settings dialog such as turning off prefetch, geolocation (which can now be turned off in settings as well) etc.
The other thing is that Firefox is open source and numerous forks strip out things like telemetry (useful for debugging but dangerous to those with state level opponents), DRM support, anything related to ads or Google, and so on. Librewolf seems to be frequently updated and comes with Ublock origin by default. If nothing else you can put everything through Tor and use Torbrowser. Their devs are experts and routinely remove dangerous features that for us are antifeatures.
One thing Mozilla could do that would help is this: the existing "enhanced tracking protection" could contain an option to turn off everything from ad measurement to DRM playback to telemetry with a single checkbox.
If I have to set up Firefox from scratch, it takes me well over an hour to interate through all the problematic features and turn them off. Given this, for my purposes I should probably use one of the forks so long as it gets the security updates quickly.
I do find it interesting that due to the volume of malware (e.g. ransomware) distributed as ads, even the FBI now recommends blocking ads. Given the source, that REALLy says something.
Also note that if Firefox dies and Chrome and its forks get a monopoly, Google gains the ability to enforce ManifestV3 on all extensions, this limiting the number of hostile servers any adblocker can block. The only way to block all ads on Chrome will be systemwide adblocking for the entire network. This used to be easy with the /etc/hosts file on Linux but that does not work with DNS over https unless that is moved from the browser to the system network stack so the system can filter it. There's also the "pi-hole" approach, and similarily on Android phones Tracker Control uses the VPN interface to filter traffic. Browsers are not officially supported but it still works for fine-grained blocking of unwanted servers.