Invisible close button of browser

No. You cannot hide it.

Though for any new window that you open from any event of the page, you can hide the titlebar though but again for it, you need to have fullscreen mode. Look here for the parameters: MSDN: Window.Open method[^]

Like all others have said, NO you can not do that.

Now, think about for a minute. Why do you want to do that? Even if there is a way to do it, how would you close the window? May be you are thinking to add your own 'Close' button. Ok so what did you achieve by removing a build it and adding your own. May be your argument is you want to do something before the window is closes. In that case the right approach is not to remove then add your own, rather you want to listen to the window closing event. Then you can do whatever you want to do before the window is closed.

Now, before you go head and ask the question, there is no clean way of listening to window closing event in web browsers. but you can go that far by onbeforeunload [^]