My wife's laptop has the Windows 10 upgrade. Firefox 40.0 works fine on the laptop. I have a desktop PC that is four years newer than the laptop, that also has the Windows 10 upgrade. I'm still having problems with the title bar not showing the X to close, and no minimize or maximize buttons. If I go to full screen I get the title bar, but it's on my tabs bar. Pages on the desktop don't render properly. Part of the page is missing. I have uninstalled and re-installed 40.0 three times, same problem. Why would it work on a five year old laptop and not on a year old desktop? it doesn't make sense. I guess 40.0 is a work in progress?