Comment 4 for bug 1599234

You can also use 'allow-sandbox: true' in the browser-support interface to use the setuid sandbox in webbrowser-app. snapcraft is correctly stripping this, but you can unsquash, reset these bits and then run 'snapcraft snap ./squashfs-root' to recreate your snap.

This is not ideal and the userns sandbox is preferred, but it can be used to unblock yourself for now.