Or for user level application that is not available as flatpak.
I see it:
- rpm-ostree for system level programs - like e.g. network packet analyzer Wireshark, disk encryption tool VeraCrypt etc. that requires root access to the computer program to work
- distrobox (BoxBuddy GUI tool) for user level programs (that are not in flatpak or does not work the best in flatpak).
Distrobox may be difficult to use for beginner level, but there is BoxBuddy that is GUI tool that hides all of the complexity of distrobox in simple to use GUI. Few days ago I have written detailed instructions how to install ART via BoxBuddy. I think it should be clear how to install Firefox using BoxBuddy from those instructions.
Distrobox (and BoxBuddy) creates a container for all of the software that will be installed and from container it allows to access /home/“user” directory from your Blufin host machine.