(mainly, it was the fact that the installer finally included firmwares out of the box which made installing much, much easier on laptops)
Because i want updated packages, the first thing i do is enable backports (otherwise i think that trixie still comes with kicad 5? hugh!) and do a full upgrade.
as for firefox, debian's repositories use firefox esr, which is why you are still on 128. There are instructions on firefox's site on how to switch to the regular release channels, just do that. If you can't trust firefox's own sources i don't know how you can trust debian's.
Debian + KDE is my favourite combo. I don't do anything different for desktop. When there was the debian 13 freeze i simply waited a couple of days, edited the sources to point at trixie and did a full-upgrade and an autoremove to clean old stuff. That's it.