When I had to test a change in another macOS version, I naively copied the `Nightly.app` to another computer, just to find out it silently fails (because of symlinked libraries) and it took a while (and external help) to figure that out.
This change instructs developers to package and use the `.dmg` instead when they want to do that, sparing the frustration and incentivizing testing in different systems.
Differential Revision: https://phabricator.services.mozilla.com/D195319
7534bdc7dc