I can see why you'd think that but in practice I assure you that your concern is unwarranted. I've been using Nightly Firefox exclusively for almost ten years and I honestly can't remember it ever crashing (excluding the times when I was manually futzing with experimental about:config flags back in the electrolysis days).

As for the developer edition, it's literally the version that they expect web developers to use; it's not half-baked software by any means.