It seems that you need to use a signed script if you wish to unconditionally close a browser window using the window.close() method. Netscape offers their "signtool" utility for signing scripts, but I'm using Internet Explorer (and I don't want to install Netscape). How can I create a signed script, given these circumstances? Alternatively, is there another way of closing a window that doesn't require a signed script?
Well you can close a window by just saying window.close(); but this will generate an alert message which cannot be avoided if you do not sign the code.
Note in NS4.7 if you access the web page which has the code for closing the browser as the first page then the browser will close without the alert being flashed i.e. this page should be the first page you visited after u opened the browser instance. But if you visit some other url's and then come to this page then the alert message will be flashed.
Note regarding code signing, you can also go for some third party CA like Verisign. For further references refer www.verisign.com.