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.

"Stable" doesn't necessary medan that it is secure, from an end-user perspective.

Do you have any stories or articles that corroborate that nightly is less secure?

You can use unbranded builds which are pretty much identical to the stable releases but let you use unsigned extensions.

https://wiki.mozilla.org/Add-ons/Extension_Signing#Unbranded...

The Developer Edition is not a nightly build, it’s a beta build, so there has been some testing (Before I switched to stable, I only once had an issue). Your point stands though.