The standard package format is through APT (Advanced Package Tool).
Flatpak and Snap are both alternatives to APT. They both are more limited in user control.
On GnuLinux, we use sudo which sandboxes Root from the user space.
Flatpak and Snap both snadbox applications from root and from the user space, thereby double sandboxing it. Due to this, Snap and Flatpak both struggle to access system files when necessary to do so.
There is good reason to favor Flatpak over Snap:
Flatpak is more featured and versatile, allowing you to use Flatseal to manage permissions and create access points for an application.
You have a third option: Remove the snap and flatpak versions and install a standard APT supplied Firefox Build: