On the whole, people using their software just to go about with their lives don't notice pointless UI changes of the scale you're talking about (changing the ap

On the whole, people using their software just to go about with their lives don't notice pointless UI changes of the scale you're talking about (changing the appearance of tabs). They don't even know what parts of the window are controlled by the application and which parts are controlled by the web page (if they even understand that distinction), and web pages change their UIs a lot faster than Firefox does.