Be aware that any configurations you do inside a running firefox will “fingerprint” you.
That’s because the first time you run firefox, it creates a random profile number and all your settings go under that profile number.
So if you run it in an AppVM, make all of your changes, then base disposables on that AppVM, every disposable run will obviously be the same individual.
If you don’t care about that, fine. Otherwise, there are methods of pre-configuring Firefox before you run it for the first time–the sort of things employers do to their employees’ provided systems. They’re complicated but not completely impenetrable.
Here is a setup that uses many of these methods, though you don’t have to do everything they do. (It’s an educational read, that’s for certain.) But with this method you can configure things in your template without ever running firefox and creating a fingerprint. Then disposables based off of it will have different identities, and so will persistent AppVMs.