I think this about lots of products or programs. I doubt anyone complained about the tabbed interface of Firefox rather than other things but yet a considerable

I think this about lots of products or programs. I doubt anyone complained about the tabbed interface of Firefox rather than other things but yet a considerable amount of time and resource was spent on changing the UI. Ditto for GMail, Microsoft Office, Windows etc. I know your designers tell you that we need to look "fresh" but you can do that with minimal tweaks, most people would rather a stable codebase that just works and doesn't cause surprises or bugs imho.