“How long does it take to build, unit test, performance test, and QA check a new Firefox release on every supported release of macOS, Windows, and Linux platform?” is absolutely a question that outraged users are trying not to confront. You’re right to ask it, so don’t let the downvotes get you down.

Presumably the testing burden for a preference update using Normandy is smaller, as (and I’m guessing wildly here) fewer things can be altered with Normandy and therefore testing can be simplified to exclude, for made-up example, “the code-signed binary can be executed on all platforms”.