After creating a fresh installation of Ubuntu 24.04, I installed DEB Firefox from APT by following Mozilla’s instructions from here. But I noticed that it was secretly replaced with Snap Firefox. I was able to verify this by checking the About Firefox page. This is the third time I noticed this.
It just occured to me that if you want to use Ubuntu without snap, you could uninstall the snap package itself (I’m not on Ubuntu, so you might need to find it), then put a ‘hold’ on the package to prevent it being reinstalled. That should, in turn, prevent any package versions that use snap from being installed.
Initially uninstalling snap might require removing any packages that use it, but that’ll tell you what you need non-snap versions of.