A third-party is less likely to have the first-party's motives, which makes a huge difference. Something blatantly stupid happens, there's a better chance of putting a stop to it before it can cause any harm and maybe even gives a little leverage to get the first-party to revert.
Only the trustee changes, so I still can't parse your concern. You don't trust Mozilla to RECONFIGURE (!) or REPLACE (!!) your software unbidden. You trust Canonical or Red Hat or whoever. And that changes what?