Firejail has some big security flaws. There us bubblejail, which uses the way better bubblewrap also used for Flatpaks.
But the Bubblewrap and Flatpak Situation is quite complex. Flatpaks, as well as Podman containers, require user namespaces. Through these namespaces programs can get privileged access to system components, which is why secureblue now has bubblewrap-suid installed.
bubblejail maybe uses that binary already, or it needs to be patched too.