I hope I am understanding you correctly: The name in the browser window (by which I think you mean the title at the very top of the browser) has no relation to the name of the file document - per se. At any rate, all you have to do is add whatever name you want in between the title tags "
<title>Put here anything you want.</title>
The title tag is located in the header of your html code (towards the top). This is what displays in your browser window. Let me know if I missed your question.