Cannot remove pre-installed apps

[isa-khibinskiy]

Hello! Is there any way to remove pre-installed packages, i.e. Firefox. I tried several ways, but nothing worked out. Discover works with flathub only. "blend remove" says "remove" is a wrong argument. "pacman" doesn't work. "system remove" says Firefox not installed, but it actually is.

[isa-khibinskiy]

I partially solved the problem. If I add a command "pacman -Rs <some_package>" into system.yaml and re-build the system with "akshara update", then it's ok. But if I remove the command from the file and re-build again, the package is back. So I got a new question. Where's the list of pre-installed packages? And can I edit it?