Who cares? The purpose of a file selector is to select a file, not look like every other file selector in existence. Even on Windows, the Office file selector looks nothing like the Photoshop one, or the Firefox one, or the Notepad one.
At least in open source, you can hack it however you want. In fact, its fairly simple to make Firefox use the KDE file picker: Enter "about:config" in the address bar, look for the "ui.allow_platform_file_picker" key and change its value to "false". ( http://www.gentoo-wiki.info/HOWTO_Integrate_Firefox_with_KDE... )
Edit: I was incorrect, the method I linked won't make firefox use the KDE picker, just an alternate gtk picker. But there are ways that can be found with a little bit of googling.
At least in open source, you can hack it however you want. In fact, its fairly simple to make Firefox use the KDE file picker: Enter "about:config" in the address bar, look for the "ui.allow_platform_file_picker" key and change its value to "false". ( http://www.gentoo-wiki.info/HOWTO_Integrate_Firefox_with_KDE... )
Edit: I was incorrect, the method I linked won't make firefox use the KDE picker, just an alternate gtk picker. But there are ways that can be found with a little bit of googling.