I understand your point, but I think it's an exaggerate view. I am happy to admit that if there's a good reason a rule should be broken, then it's ok too: but you need to know what to do. Like all rules, once you understand them and know what you are doing, then it may make sense to break them.

But imagine a user that faces an interface that looks familiar but it's all different. Maybe the most external button in the title bar expand it. Or something that looks like a button has to be double clicked instead of clicked once. The point of having a consistent UI for the whole OS is that the user doesn't need to relearn a new interface for each product.

That said there are cases where the current UI is not good enough, maybe because the developer has a new, never done before idea. Then it's ok. Apple does it, for example, as do other mac developers.

The other exception is when it's a very specialised piece of software that is not for the masses but for a very specialised niche. I consider CAD applications, Photoshop and Aperture are like that. It's not _as_ useful to use the same look because they are software that has to be learnt anyway.

However... Firefox and Chrome do try as hard as possible to conform to the UI interface so I don't follow your examples there. And iTunes is loath by everyone as a awful piece of UI, so I wouldn't use it as an example either.

Similarly many people (at least on the Mac) hate the completely alien look Photoshop has, or Office. Microsoft did put a lot of effort with OS X to follow OS X conventions, and despite Photoshop not being a mass market product, Adobe has preferred to have a uniform cross-platform interface, and there's a lot of complaints for that.

So yes, if you have a novel interface requirement then you are more than welcome to break the OS standards. But otherwise if there's no need (from a user perspective) I don't think it's a good idea.