What a comment! You made a binary discussion from a nuanced one. The question is whether an attractive UI (which, surprise, matters to many people) is worth focusing developer effort. Several comments in this thread advocate that non-native UIs look tacky, and that it would do well for the product to have native rendering.
As an aside, it's the no. 1 reason I don't use Atom: An ugly, slow UI that doesn't render native elements.
So no, it's not indefensible. I think your conspirator's OP comment "As a non-OSX user, I don't care about your UX" is more vain.
> I think your conspirator's OP comment "As a non-OSX user, I don't care about your UX" is more vain.
Sure it's vain. We all have personal priorities. People suggesting that Mozilla spend time developing the perfect OS X product are expressing their priorities as well.
I could say that I'm a BeOS user and I really think that Firefox should have a fully-integrated native UX because the way a product looks and works is important. But no one cares about BeOS UX because they're vain.
It looks like OS X users are the only ones who really care. Windows users have been dealing with non-standard UIs since tabs first stopped being MDI, and, comparing Chrome's adoption with how it looks, they're mostly fine with them. Linux users are mostly just straight-up crazy and Firefox is fine for them. Smartphone users have seen more non-standard than standard UIs and it doesn't seem to have been a problem for the Facebook app. The question is then is it worth caring as much about OS X UI, or is it more useful to make a better product for the 80+% of users who don't use OS X?
As an aside, it's the no. 1 reason I don't use Atom: An ugly, slow UI that doesn't render native elements.
So no, it's not indefensible. I think your conspirator's OP comment "As a non-OSX user, I don't care about your UX" is more vain.