For FF and Tor browser launcher the situation is similar. But they don’t even try to replace the namespace sandbox with flatpak-spawn. So you lose namespaces and chroots. This leads to weakened site isolation, weakened protection of the browser’s files (history, cookies, …) and also to less protection of the host OS. In the issue tracker about this topic, FF employees stated that they are aware of the missing namespaces and chroots, but downplay their importance. Side-note: They also never implemented a SUID sandbox, so users with deactivated unprivileged user namespaces have the same problem with missing namespace+chroot sandbox even though the about:support page makes you believe otherwise.