There is no link, implied or otherwise, between allowing a harmless, off-by-default, accidentally visible extension and "spyware in my browser". This extension wasn't just harmless for your privacy, but it was intentionally, specifically harmless.

Yes, it does highlight that Mozilla isn't a perfect, flawless entity that never makes mistakes, but the process protected your interests exactly the way it was designed to do and you already knew that anyway.

If the issue is that Mozilla sometimes pushes imperfect code, why is everyone harping about this absolutely harmless instance and not, say, one of the hundreds of actually meaningful security vulnerabilities? Why are people fixated on this totally arbitrary and counterproductive metric of the fact it showed up under the "extensions" header, rather than a metric of whether it has literally anything to do with the interest you're trying to protect?

If you only want to run code written by perfect entities, fine, go ahead. But you shouldn't have been using Firefox in the first place, and you certainly shouldn't be making unsupported moral claims about them for not hitting impossible standards.