apt "pinning" is the process you're looking for. This allows you to prevent reinstallation of snapd and prefer other sources for packages, e.g. Firefox from Mozilla's PPA.
So Ubuntu doesn't provide apt packages so if I want to use apt I have to muck around with PPAs? I don't want to have to add a PPA for every software I install. This is why Debian is better for my use case -- all I have to do is apt install and boom I have the Debian package installed. All this works out of the box on a Debian installation.
Sorry, but this is not true. It's claimed you can use pinning, but at least on my installation, it didn't work no matter what documentation I followed. There was literally no way to stop it from silently switching to the Firefox snap. Well, installing Linux Mint fixed it, but that's not really the same thing.