Sandboxing Chromium Snap without FireJail

I'm a Firefox user who uses Chromium for certain google websites.

I like to run Chromium in a sandbox so that the "Downloads" folder is the only file system location Chromium can see.

In Ubuntu 19.04, I could achieve this with:
sudo apt install chromium-browser firejail ; firejail chromium-browser

In Ubuntu 19.10, Chromium is only offered as a snap package:
https://bugs.launchpad.net/ubuntu/+source/chromium-browser/+bug/1847092

Firejail, doesn't work with Chromium's snap package installation:
https://askubuntu.com/questions/1178995

The snap installation's degree of isolation seems to be controlled by the developer of snap package.

Since firejail no longer works for achieving this degree of isolation, I'm requesting that the Snap Package Maintainer (of Chromium), provide an alternative installation that only gives Chromium access to the "Downloads" folder exclusively.

ProblemType: Bug
DistroRelease: Ubuntu 19.10
Package: chromium-browser (not installed)
ProcVersionSignature: Ubuntu 5.3.0-13.14-generic 5.3.0
Uname: Linux 5.3.0-13-generic x86_64
NonfreeKernelModules: zfs zunicode zavl icp zcommon znvpair
ApportVersion: 2.20.11-0ubuntu7
Architecture: amd64
CurrentDesktop: ubuntu:GNOME
Date: Mon Oct 7 08:15:38 2019
InstallationDate: Installed on 2019-10-06 (0 days ago)
InstallationMedia: Ubuntu 19.10 "Eoan Ermine" - Beta amd64 (20191001.2)
ProcEnviron:
 TERM=xterm-256color
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: chromium-browser
UpgradeStatus: No upgrade log present (probably fresh install)