Yes, that’s why I installed it from unstable. The ESR version is an older version with added security patches. I’m not sure, why exactly they are doing it like that and I don’t think it’s a good idea. I’d say a browser should be as up to date as possible for both, bug fixes AND new features. But it worked flawlessly using the “unstable” firefox package. Another option would be the flatpak, but that’s not that well integrated into the system - last time I tried that, the font rendering in the browser was awkward. I use some other flatpaks though, most notably gimp and inkskape which work really well and are very up to date that way.